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Unmanned Spaceflight.com _ Private Missions _ The Pioneer Anomaly
Posted by: remcook Aug 16 2005, 04:27 PM
http://www.planetary.org/news/2005/pioneer_anomaly_faq.html
The planetary society may be checking it out...
QUOTE
The Planetary Society has committed to raise the funds to preserve the priceless Pioneer data from destruction.
After years of analysis, but without a final conclusion, NASA, astonishingly, gave up trying to solve the "Pioneer Anomaly" and provided no funds to analyze the data. The Pioneer data exists on a few hundred ancient 7- and 9-track magnetic tapes, which can only be read on "antique" outdated computers. The agency is going to scrap, literally demolish, the only computers able to access and process that data in the next few months!
Posted by: remcook Aug 16 2005, 04:40 PM
Some background reading...
http://arxiv.org/find/astro-ph/1/ti:+pioneer/0/1/0/all/0/1
Posted by: tedstryk Aug 16 2005, 06:53 PM
Won't New Horizons be spin stabilized when not in encounter mode?
Posted by: remcook Aug 16 2005, 07:43 PM
Quote from alan stern:
QUOTE
Yes, we spin most of cruise, stopping only rarely. It costs fuel that we want to hoard for encounters and KBO DeltaV. And yes, our radio science team hopes to look for
the Pioneer anaomaly. Contact Len Tyler or Ivan Linscott at Stanford.
in the new horizons thread:
http://www.unmannedspaceflight.com/index.php?showtopic=675&st=20
so some more things to look forward to
Posted by: Richard Trigaux Aug 17 2005, 06:37 AM
Could not the Pioneer tapes be saved on a more modern support, before scraping the computers which can read it? So far as we know there may be still valuable data to infer from them, especially with the affair of the "pioneer anomaly".
Much was already said about this anomaly:
-the gravitaion law working differently at great distance...
-effect of cosmological dark matter surrounding the sun...
or simpler:
-systematic mistakes somewhere into the measurement chain.
Perhaps the NASA and many scientists prefer the second set of explanations. But so long as the first set cannot be completely ruled out, the question remains open.
Posted by: Jeff7 Aug 17 2005, 07:09 PM
QUOTE (remcook @ Aug 16 2005, 11:40 AM)
Some background reading...
http://arxiv.org/find/astro-ph/1/ti:+pioneer/0/1/0/all/0/1
I looked at some of those things, but still am not quite clear on what this anomoly is.
And what's up with saving this? I think I missed out on this stuff.
It looks like the Pioneers have long stopped transmitting, but the data hasn't been analyzed yet, and now NASA wants to destroy the computers that can read the tapes? Is that the gist of it?
Posted by: remcook Aug 17 2005, 08:09 PM
QUOTE
It looks like the Pioneers have long stopped transmitting, but the data hasn't been analyzed yet, and now NASA wants to destroy the computers that can read the tapes? Is that the gist of it?
that's what I understand yes...
The anomaly is basically that the pioneer spacecraft (I think it was seen in Ulyssus and Cassini as well) accelerate slightly different than what one would expect from our understanding of gravity.
Posted by: deglr6328 Aug 17 2005, 11:10 PM
QUOTE (remcook @ Aug 17 2005, 08:09 PM)
that's what I understand yes...
The anomaly is basically that the pioneer spacecraft (I think it was seen in Ulyssus and Cassini as well) accelerate slightly different than what one would expect from our understanding of gravity.
Not Cassini but Galileo. Cassini is 3-axis stabilized (thrusters). Galileo was spin stabilized. The error introduced by the use of thrusters basically washes out any hope of seeing any other miniscule anomalous effects.
Posted by: Richard Trigaux Aug 18 2005, 06:59 AM
As far as I understand from readings in the press, the Pioneer probes (ant others) would slow down slighty more than expected from only the Sun gravity. This led to some interesting but far reached speculations.
Some asked if the gravity law was not exactly 1/R2.
The most consistent speculation is that, like the galaxy shows an excess (sometimes ten times) of invisible mass, called dark matter, the solar system may have some too (although much less, a fraction of a %). From close to the Sun, we feel only the Sun's attraction, but further in space we feel the Sun's more the dark matter's attraction. This could be explained if the dark matter is made of low energy subatomic particles; many would orbit the galaxy, with speeds in the 200km/s range. Some would orbit the Sun with still smaller speeds in the km/s range.
But the measurement of the anomaly is based on many far-reached and difficult estimates, such as the toss of sun's light on the space probe, or gaz leak from the reservoirs. A slight error or false assumption, and the result would be very different. This is why the Pioneer anomaly did not upset the science community. A precise measurement of this anomaly would perhaps do.
Posted by: Bob Shaw Aug 18 2005, 08:24 AM
QUOTE (deglr6328 @ Aug 18 2005, 12:10 AM)
Not Cassini but Galileo. Cassini is 3-axis stabilized (thrusters). Galileo was spin stabilized. The error introduced by the use of thrusters basically washes out any hope of seeing any other miniscule anomalous effects.
So presumably the New Horizons vehicle won't be stable enough, for long enough, either...
Posted by: The Messenger Aug 26 2005, 09:08 PM
QUOTE (Richard Trigaux @ Aug 17 2005, 11:59 PM)
As far as I understand from readings in the press, the Pioneer probes (ant others) would slow down slighty more than expected from only the Sun gravity. This led to some interesting but far reached speculations.
...
But the measurement of the anomaly is based on many far-reached and difficult estimates, such as the toss of sun's light on the space probe, or gaz leak from the reservoirs. A slight error or false assumption, and the result would be very different. This is why the Pioneer anomaly did not upset the science community. A precise measurement of this anomaly would perhaps do.
Painstaking and careful analysis is a more exacting description.
http://arxiv.org/find/astro-ph/1/au:+Turyshev_S/0/1/0/all/0/1
http://arxiv.org/abs/gr-qc/0104064
http://arxiv.org/abs/gr-qc/9906112
Anderson, Nieto & Turyshev's paper- rebuttal - papers with the astrophysical community spans more than a decade now, and signatures of the anomalies have been found everywhere they have found the time and money to look for them.
The community should be giving this type of research highest priority -
Nowhere is it written in stone gravity behaves exactly as was predicted and observed a more than a century ago. If the observational data indicates otherwise, why are we so certain the status que is the status correct?
Posted by: antoniseb Aug 26 2005, 10:42 PM
QUOTE (The Messenger @ Aug 26 2005, 04:08 PM)
The community should be giving this type of research highest priority
The highest priority? I think finding all substantial Earth Crossing asteroids would be more important. Basic exploration of the Solar System should be more important. Looking for extra-solar planets should be more important. Galactic census missions should be more important. Studies of Sgr A* and the things orbiting it should be more important. Studies of distant Type 1a Supernova should be more important. etc.
The ESA has considered launching a probe specifically to measure this effect with greater precision, but it didn't get funded.
Perhaps you could tell us how you would probe this phenomenon, and what the various outcomes would tell us? Then we can talk about priorities.
Posted by: The Messenger Aug 29 2005, 05:25 PM
QUOTE (antoniseb @ Aug 26 2005, 03:42 PM)
The highest priority? I think finding all substantial Earth Crossing asteroids would be more important. Basic exploration of the Solar System should be more important. Looking for extra-solar planets should be more important. Galactic census missions should be more important. Studies of Sgr A* and the things orbiting it should be more important. Studies of distant Type 1a Supernova should be more important. etc.
The ESA has considered launching a probe specifically to measure this effect with greater precision, but it didn't get funded.
Perhaps you could tell us how you would probe this phenomenon, and what the various outcomes would tell us? Then we can talk about priorities.
Two things:
1) I would take the mother-and-hen approach suggested by Nieto. Pioneer 10 & 11 demonstrated the virtues of simple, spin stabilized, thermally balanced probes. I would add a lot of health monitoring gear, but otherwise the probes should be very simple. They should have transmitters capable of using both phase-locked loop and ultra-stable oscillator ranging frequency control, multiple bands.
There should be at least two different types of chicks - one designed with a great deal of solar drag, the second fairly streamlined. Placed into identical trajectories at the same time, this would allow differentiation of unknown forces from solar wind effects. Perhaps even better would be ‘umbrella chicks’ that could trade-off between solar sail and coast modes, thus keeping the clutch together.
The mother should hover close enough to calibrate and study emissivity and radiation, but distant enough not to disturb momentum.
2) If one assumes the Pioneer anomalies are real and not artifacts, there should be supportive evidence, and many fundamental implications.
The solar wind may not be the only force moving objects away from the center of the solar system. Anderson had to add a linear component to the solar wind to model the acceleration of Galileo and Ulysses: http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf p21:
QUOTE
The radio Doppler and ranging data can be fit to the noise level with a time-varying solar constant
in the fitting model [82]. We obtained values for the time-varying solar constant determined by Ulysses
FIG. 10: Galileo best fit Doppler and range residuals using CHASMP. navigational data during this south polar pass [81]. The inferred solar constant is about 40 percent larger at perihelion (1.3 AU) than at Jupiter (5.2 AU), a physical impossibility!
We sought an alternative explanation. Using physical parameters of the Ulysses spacecraft, we first converted the time-varying values of the solar constant to a positive (i.e., outward) radial spacecraft acceleration, ar, as a function of heliocentric radius.
(my bold)
Throw a spring constant into elliptical orbits, as Anderson did to model Ulysses, and all hell breaks loose. Fly-bys and orbits don’t return correct planetary masses, long distance navigation breaks down, and gravity anomalies crop up everywhere.
Such a force
is consistent with known observational facts. Figuring out if it is real should be given highest priority.
Posted by: algorimancer Aug 29 2005, 05:40 PM
It seems to me that a simple means of checking this notion would be to track long-period comets (many of them). No spacecraft required
Posted by: The Messenger Aug 29 2005, 06:12 PM
QUOTE (algorimancer @ Aug 29 2005, 10:40 AM)
It seems to me that a simple means of checking this notion would be to track long-period comets (many of them). No spacecraft required
Too wide of error bars - Comets are always outgassing, changing in mass, color, orientation. We are looking at accelerations of less than 60 ppm.
Also, Radar tracking has proven to be less accurate than physical modeling suggest, as we learned from the Mars Climate orbiter and Polar Lander...perhaps Anderson's unmodeled force is the culprit.
Posted by: edstrick Aug 30 2005, 08:52 AM
Climate orbiter was not radar tracked, it was transponder tracked. You get precise distance, but have to model angular position on the sky from indirect data. One way to get precise relative position in the sky is differential interferometry, where one vehicle, say a mars orbiter, is a reference source, and the approaching vehicle's position relative to the reference can be measured.
The problem with Climate orbiter was not with the tracking data, it was modelling the trajectory based on that data when bogus information <incorrect spacecraft peturbation values from the momentum wheel offloading with thruster firing) was included in the solution. The nav team had recognized and been bothered the entire flight by considerably (several times?) larger trajectory calculation variations than normal, but not been able to find a cause of the error with available time and resource.
Polar Lander wiped out due to either 1.) a programming error in the descent software that was almost guaranteed to eat their lunch. or 2.) any of considerable number of design defects that added risk to the landing but weren't "smoking gun" errors.
The Pioneer anomaly is just that.. it's a departure of observations from very precise, but known imperfect calculations. We don't know if there's a physical something based on "deep" important physics, or if our engineering models of non-gravitational forces on the spacecraft are subtly wrong.
It will cost at least a few hundred million dollars to fly a mission that will convincingly and unambiguously prove an "important" physics cause is either present or not, and *PRECISELY* measure that effect if it exists as a function of distance from the sun. *** NOT TRIVIAL ***.
There are a lot of other research proposals and proposed space missions with equal or greater chances of testing and getting an important answer to "deep" physics questions that would cost the same or less than a Pioneer Anomaly mission. The best strategy is to pick the strongest tests with the greatest likelyhood of surprise, for the least amount of money and do or fly those..... and to pick tests that test fundamentally different possible suprises in deep physics. Things like dark matter detection experiments, gravity wave observatories, Dark energy investigations have far more chance per doller of real surprises than a pioneer anomaly mission. We need to keep it as an open question with the possibility of a mission, but right now, it seems a high risk, probably low yield mission for the money.
Posted by: Mongo Aug 30 2005, 07:12 PM
QUOTE (edstrick @ Aug 30 2005, 08:52 AM)
There are a lot of other research proposals and proposed space missions with equal or greater chances of testing and getting an important answer to "deep" physics questions that would cost the same or less than a Pioneer Anomaly mission. The best strategy is to pick the strongest tests with the greatest likelyhood of surprise, for the least amount of money and do or fly those..... and to pick tests that test fundamentally different possible suprises in deep physics. Things like dark matter detection experiments, gravity wave observatories, Dark energy investigations have far more chance per doller of real surprises than a pioneer anomaly mission. We need to keep it as an open question with the possibility of a mission, but right now, it seems a high risk, probably low yield mission for the money.
The problem with a 'dark matter' mission is that the putative dark matter is entirely hypothetical, and may not (I would say probably doesn't) exist. Stanley Milgrom's MOND theory or Jakob Bekenstein's TeVeS theory seems to me to explain the observations in question much more easily than any dark matter theory does. There are also indications that the effects ascribed to 'dark energy' may also be a natural result of a full MOND or TeVeS theory.
http://xxx.lanl.gov/abs/astro-ph/0504130
On the other hand, the so-called 'Pioneer Anomaly' appears to be genuine. The alternative explanations (solar wind, asymmetrical thermal radiation, etc.) appear to be several orders of magnitude too small to adequately explain the observed acceleration. I personally would say that a proper investigation of the 'Pioneer Anomaly' would be at least as important as Gravity Probe B, and could be mounted at a reasonable cost too. The spacecraft itself would be relatively inexpensive; the biggest cost would be the launch vehicle.
Here are links to papers discussing possible approaches to a mission:
http://xxx.lanl.gov/abs/astro-ph/0504634
http://xxx.lanl.gov/abs/astro-ph/0409373
http://xxx.lanl.gov/abs/gr-qc/0409117
Bill
Posted by: Bob Shaw Aug 31 2005, 11:28 AM
Bill:
Your links, er, don't!
Bob Shaw
Posted by: Mongo Aug 31 2005, 02:45 PM
That's strange; I just clicked on them and they sent me to the reports that I had referenced...
If they still don't work, I suppose that you can just go to
http://xxx.lanl.gov/find/astro-ph
and do a search for 'Pioneer Anomaly'. Or else just type out the links on your address bar.
Bill
Posted by: Bob Shaw Aug 31 2005, 03:42 PM
QUOTE (Mongo @ Aug 31 2005, 03:45 PM)
That's strange; I just clicked on them and they sent me to the reports that I had referenced...
If they still don't work, I suppose that you can just go to
http://xxx.lanl.gov/find/astro-ph
and do a search for 'Pioneer Anomaly'. Or else just type out the links on your address bar.
Bill
Bill:
I promise, linky no worky.
________________________________________________________
Access Denied
Sadly, you do not currently appear to have permission to access http://xxx.lanl.gov/find/astro-ph
If you believe this determination to be in error, see http://xxx.lanl.gov/denied.html for additional information.
_________________________________________________________
Bob Shaw
Posted by: Mongo Aug 31 2005, 03:57 PM
QUOTE (Bob Shaw @ Aug 31 2005, 03:42 PM)
I promise, linky no worky.
Okay, I'll try posting the files directly to the board. Hope this works.
The first file is the 'dark energy' in TeVaS paper. The other three are the 'Pioneer Anomaly' papers.
Bill
Posted by: The Messenger Aug 31 2005, 06:56 PM
I am at least as interested in the flight path eccentricities of Odysseus, Galileo and Pioneer 6 as the Pioneer 10 and 11. While the Pioneer probes indicate an acceleration towards the sun, an unsolicited acceleration away from the sun had to be used to model the paths of Odysseus and Galileo, and one of a greater magnitude: ~1x10^-8m/s^2.
Likewise, I mentioned the navigational problems associated with the Polar Lander and Climate orbiter, not because of the failure modes, but because of the difficulty navigators had both predicting and tracking the probes – with or without a unit conversion error.
After the Climate Orbiter failed to achieve a non-intersecting orbit, two teams of navigators worked on the flight path of the Polar Lander. Each time they tried to model and predict solar wind effects, they were frustrated – they could not correlate the small force corrections due to the solar wind with the path of the probe.
On both missions, NASA tried to use triangulation as well as the Doppler ranging data, and triangulation yielded surprisingly unsatisfactory results.
Please allow me enough latitude to use a hypothetical to demonstrate why I think we must track down the exact causes of these small force and/or navigational errors. Assume the forces are real, and assume they are caused by a gravitational equivalent to a change in the permeability-of-free-space that is a function of mass. This would mean that a probe moving towards the sun would be slowed as more energy is stored in a stronger ‘mass field’ nearer the sun.
The Newtonian equation for velocity then becomes a function of total proximal mass, not just the mass of the object in motion (Ek=Mv^2/2f(x) where f(x) @ 1 AU = 1, and becomes larger as the object approaches the sun, leaving more energy in the potential energy pool (Remember, this is ALL HYPOTHETICAL and the force changes are very small and tightly constrained.)
Look what would happen: As a probe approaches the sun, less potential energy is 'released' as kinetic. The velocity increases at a slightly slower rate than Newtonian predictions. Leaving close proximity to the Sun, the probe would require slightly less energy to achieve a greater acceleration, returning the probe to the predicted path. This is EXACTLY what the residuals look like in the Pioneer 6 pass near the limb of the sun, peaking (slowing) at closest proximity to the sun. Likewise, the 1/r ‘spring constant’ Anderson used to model the Solar wind effects upon Odysseus and Galileo follow this model.
There is more: If more potential energy is stored in a more massive environment, probes to Venus are proportionally slowed, while probes to Mars would experience a slight acceleration, achieve a slightly different orbit. This would cause us to overestimate the mass of Venue, and underestimate the mass of Mars. When we interpret the orbital gravimetric data, the smaller accelerations near the mountain peaks on Venus would then appear as negative gravity anomalies, and likewise, valley floors would appear as positive anomalies. This is what we observe.
On Mars, the situation is exactly opposite: The increase in the transfer to kinetic energy would cause us to underestimate the mass of Mars from orbiters, so the mountain peaks would be interpreted as positive gravity anomalies while valley floors would appear negative. This is also precisely what we observe.
There is more.
We now have gravity maps of Mars from distances varying from 300 to 800 km, but the 800 km data cannot be reconciled with the 300 km maps. The 300km data showing greater anomalies. The moment of inertia for Mars appears to be different if ranging data to the surface probes (Pathfinder and Viking) is used than the inertial moment necessary to explain the orbital gravity anomalies.
All of the Martian probes have landed at higher velocities than expected and, entered at higher attitudes. All descent trajectory models have required a thinner-than-expected upper atmosphere, and high surface winds.
I can go on and on, but I think that you get my point: It would not take a major change in solar dynamics to produce surprising errors. I have been arguing with Jason and Bruce that the rocks, the craters, the strata, and the Doppler descent data from Huygens could be better modeled with less shear wind and more mass.
Fortunately, missions are already in progress that can disprove this hypothesis: Messenger will pass close enough to the sun that the ‘limb effect’ observed by Pioneer 6 could be repeated. MRO will provide gravity maps at 150 km – if this hypothesis is true, MRO will map greater gravity anomalies than prior orbiters that cannot be fit with harmonic extrapolations. MCO will also provide us with a good average atmospheric gradient, one that will be steeper than expected if the planet is more massive.
Finally, careful mapping of the effects of Saturn’s moons on Cassini should reveal ‘unmodelable drag’ forces and even greater gravity anomalies than Galileo found on Ganymede.
I don’t expect any degree of agreement with this assessment, but I hope I have peaked your interest in the manifold scientific data returning from the robotic planetary missions; and there just might be more to learn than mission planners dreamed, a truly revolutionary prospective of the cosmos, one just as foreign to scientific thinking today as the Ptolemic model.
Posted by: dvandorn Aug 31 2005, 07:24 PM
Hmmm... well, the effect must be very, very minor (at least in the local solar-system neighborhood), or else the planets wouldn't orbit in such a way as to generally validate the inverse-square law of gravitation.
It *does* occur to me that the inverse-square law relates to the "classic" three physical dimensions, and cosmologists are always saying that as many as 19 physical dimensions *must* exist. As far as we can tell (since we cannot directly measure anything outside of the three dimensions that are apparent to us), gravitation doesn't propogate along any of these other physical dimensions. Perhaps this is an indication that it *does* and the effect we are seeing is actually a relation between some other physical dimension(s) and the three we can perceive? This would mean that the inverse-square law could be maintained; we're just applying that law to a dimension that is not obviously connected to the three we can see.
I think it's time to start contemplating how these extra dimensions that cosmologists believe must exist inter-relate with the Universe as we observe it. Rather than assuming that these dimensions simply collapsed and vanished as energy levels decreased shortly after the Big Bang, maybe they still exist and interact with such things as gravitation... However, I think it's too early to say that this effect happens near massive bodies, and it's definitely too early to start making mass itself a variable factor, relative to its distance from other masses.
-the other Doug
Posted by: antoniseb Aug 31 2005, 09:58 PM
QUOTE (The Messenger @ Aug 31 2005, 01:56 PM)
I am at least as interested in the flight path eccentricities of Odysseus, Galileo and Pioneer 6 as the Pioneer 10 and 11. While the Pioneer probes indicate an acceleration
towards the sun, an unsolicited acceleration
away from the sun had to be used to model the paths of Odysseus and Galileo, and one of a greater magnitude: ~1x10^-8m/s^2.
Hi The Messenger,
We've interacted a few times on another forum. This is the clearest statement of what you've been trying to get to that I've seen. Thanks. I will now be trying to keep an eye on this.
Posted by: Richard Trigaux Sep 3 2005, 09:07 AM
Thanks to recent posters this thread took an interesting turn, that we could summarize that a mission specifically dedicated to the Pionneer anomaly would be potentially very interesting, but that it is not likely to fly one day.
It could become more likely if it is send with other equipments, for instance for the study of solar wind effect, interplanetary magnetic fields, etc. The overal design of such a probe could allow to measure the "Pioneer effect" with much more accuracy, or at least to prove/disprove its existence.
How could such a probe work?
Basically a test mass, a raw piece of metal, should freely navigate into the solar system, on a trajectory fleeing the sun, while being protected of any spurious accelerations: solar wind, electric/magnetic effecs, outgassing, position control, etc.
To achieve this, it would be completelly enclosed into a metal casing, while having no physical contact/interaction with it. The casing would use thrusters to lock itself on a fixed position relative to the test mass.
So the overall thing navigates as if it was in really complete vacuum, without solar wind, outgassing, etc. and it can provide accurate informations of pure gravitationnal nature, eventually different of the 1/r2 law, or accounting for unknown bodies. The info on the trajectory corrections achieved by the casing would on its side provide very accurate data on solar wind. This makes this probe more interesting and more likely to fly than just a Pioneer anomaly test probe.
The only spurious gravitationnal effect on the test mass would be... the gravitationnal field of the probe itself. Thus the test mass should be placed right at the center of mass of the probe. An error on this would produce a permanent offset that we could not distinguish from true effects. If preleminary calculations show this is a problem, we can use a better overal design: the probe is formed of three parts, linked with cables: at the centre the protective casing, and at the extremities the radio transmitters, thrusters, and any other payload useful for science (and also useful to make this mission more likely). The whole thing rotates on an axis which is perpendicular to the sun direction, right around the test mass.
This design will allow to know preciselly the centre of mass and to adjust it. But above all, any permanent offset will be cancelled, as it will pull at times toward the Sun, at times opposite to the Sun. So we can really maintain the test mass free of spurious gravitationnal effects from the probe itself.
Such a probe would be relatively light wheight, so that it could be launched on an interstellar trajectory directly from the surface of the Earth, without using gravitationnal assistance. So it could bring results after only a few years. Otherwise we can use Jupiter' assistance.
Will this design lead one day to a real experiment?
Posted by: Richard Trigaux Sep 3 2005, 10:07 AM
A rather interesting prospective explanation of the Pioneer anomaly could come from a completelly different field, from the exploration of the cosmic background radiation at 3°K by COBE and WMAP.
These two probes found results which strinkingly match the predictions of the standard cosmologic inflation theory in the very early stages of the universe, excep for some points. Here is a paper on this:
http://background.uchicago.edu/~whu/Papers/HuWhi04.pdf (I did not read it, I read the french publication in the science review "Pour la Science", french edition of the Scientific American).
Among the possible explanations on these discrepancies was evoked the possibility of a cloud of matter (dust or neutral gas) near the solar system or in orbit around it. Such a cloud would be essentially of a very low density, and thus very transparent at any wavelengh. It would emit/absorb only radiations matching its black body temperature, which is, for a free body in far space, at equilibrium with the cosmic background! This would explain that such a cloud was never detected before: only a precise measurement of the cosmic background could allow for its discovery.
If such a cloud exists, its very low density multiplied by its huge dimentions would lead to a sizeable mass, more than a planet, and even in the order of a star mass.
This would perfectly explain the Pioneer anomaly, and even the variations found on this effect (at times toward the Sun, at times opposite) according if the probe goes toward the cloud or in another direction.
Eventually a Pioneer effect probe becomes more interesting.
Posted by: remcook Sep 3 2005, 10:18 AM
some people seem to agree and applied for funding from ESA's cosmic vision 2015-2025:
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=35202
QUOTE
Title:Â A Mission to Test the Pioneer Anomaly and to Probe the Mass Distribution in the Nearby Outer Solar System
Proposed by: Orfeu Bertolami et al.
Contact Email: orfeucosmos.ist.utl.pt
[...]
Title:Â Testing the Pioneer Anomaly
Proposed by: Hansjörg Dittus et al.
Contact Email: dittuszarm.uni-bremen.de
[...]
Title:Â Experimental investigation of the Pioneer anomaly
Proposed by: C. Kiefer et al.
Contact Email: kieferthp.uni-koeln.de
[...]
Title:Â Significance of the Pioneer Anomaly
Proposed by: Claus Lämmerzahl et al.
Contact Email: laemmerzahlzarm.uni-bremen.de
[...]
Title:Â LISA Mission and the Pioneer anomaly
Proposed by: José Luis Rosales
Contact Email: JoseLuis.Rosalesesp.xerox.com
Posted by: The Messenger Sep 3 2005, 05:00 PM
Richard's proposed test of the Pioneer Anomaly is clever, and controls several variables. Unfortunately it also has the potential of introducing another new one: Shielding the test mass from the 'unknown force', especially if it is electromagnetic in nature: In this case if the results were nil, the Pioneer Anomaly could be constrained to a possible emf - but what emf?
The cloud solution is also interesting, but the two Pioneer probes were heading for opposite sides of the solar system and produced the same relative error. (Two identical clouds?) Also, Nieto and other researchers have been able to all but eliminate the Oort cloud and Kuiper belt objects as likely candidates for the PA, and this evaluation seems to apply to rouge clouds as well. (They also constrain the potential for local Dark Matter & Energy.
http://lanl.arxiv.org/abs/astro-ph/0506281
Antoniseb has started a thread to discuss second WMAP release, specifically in the context of the 'local' anomalies, and I will post a response there. As you know from my postings on this thread, I am of the opinion many quirky observations are interelated.
http://www.unmannedspaceflight.com/index.php?showforum=44
There is much to learn.
Posted by: Richard Trigaux Sep 4 2005, 07:03 AM
Messenger,
my idea was intended to detect a gravitationnal effect (or gravitationnal-like). We could modify the shielding, for instance using a transparent shield to allow for electromagnetic effects. But in this case, we shall not know if the effect is gravitationnal or electromagnetic...
Or we can make several experiments, several test mass... but the probe has only one mass center. I do not come with more "clever" designs, unless to use several concentric shields around the test mass: one metallic, shielding the test mass from EM effects, and locked on the test mass without physical contact. And around, a second shielding, avoiding solar wind but transparent to electromagnetic effects, and locked on the first shield. This may allow for a separate measurement of both three effects, gravitationnal, EM and wind effect. But this fairly complicates the design, and does not make sure that the result would be better. Especially the intermediary shield will need some thrust, and thus it will "pollute" the results of the outer shield.
So I think it will be better to keep with my first simple design, perhaps adding it sensitive electromagnetic instruments. If gravitationnal effects are ruled out, we can still check for electromagnetic effects, but they offer much less potential for interesting discoveries. (but they cost much less to search)
Thank you also Messenger for your contribution on the Oort clouds and similar. We know litle things about the Kuyper belt and Oort cloud. We usually assume they have a syymmetrical structure (a disk for the Kuyper belt, a sphere for the Oort cloud). At least they would have gained such a symmetry after rotating around the Sun for 4 billion years. If they have such symmetrical structures, they cannot have gravitationnal effects in the inner solar sytem (a hollow spherical structure has no gravitationnal effect inside).
But many things may cause such clouds to have transcient or permanent "lumps" in it:
-part of the mass is in the form of massive bodies, such as the one recently detected which is larger than Pluto. (Many trajectory calculations should be remade accounting with it). It could even exist very dark and cold massive gaseous planets very far from the Sun.
-the solar wind shockwave with the interstellar wind concentrates mass
-a spherical cloud is in orbit around the Sun
-an interstellar cloud is currently at close vicinnity with the solar system (such clouds can have mass ranging from a giant star mass to Earth mass)
-a large wandering planet is currently at close vicinnity with the solar system
A last there is one difficulty with my probe: it will only tell us what there is in one direction. If we obtain enough precision, we could try to model the effect with an 1/R2 gravitationnal field, and find the culprit. But this will take ten years, and if the probe flight path is not in a proper direction, it will not work. So ideally we should send three probes in three perpendicular directions to definitively find (or rule out) any gravitationnal effects. In practice we could send one, wait two or three years to see the results, and take the decision to send another one in a proper direction.
Posted by: jamescanvin Sep 5 2005, 12:13 AM
QUOTE (Richard Trigaux @ Sep 3 2005, 07:07 PM)
How could such a probe work?
Basically a test mass, a raw piece of metal, should freely navigate into the solar system, on a trajectory fleeing the sun, while being protected of any spurious accelerations: solar wind, electric/magnetic effecs, outgassing, position control, etc.
To achieve this, it would be completelly enclosed into a metal casing, while having no physical contact/interaction with it. The casing would use thrusters to lock itself on a fixed position relative to the test mass.
So the overall thing navigates as if it was in really complete vacuum, without solar wind, outgassing, etc. and it can provide accurate informations of pure gravitationnal nature, eventually different of the 1/r2 law, or accounting for unknown bodies. The info on the trajectory corrections achieved by the casing would on its side provide very accurate data on solar wind. This makes this probe more interesting and more likely to fly than just a Pioneer anomaly test probe.
The only spurious gravitationnal effect on the test mass would be... the gravitationnal field of the probe itself. Thus the test mass should be placed right at the center of mass of the probe. An error on this would produce a permanent offset that we could not distinguish from true effects. If preleminary calculations show this is a problem, we can use a better overal design: the probe is formed of three parts, linked with cables: at the centre the protective casing, and at the extremities the radio transmitters, thrusters, and any other payload useful for science (and also useful to make this mission more likely). The whole thing rotates on an axis which is perpendicular to the sun direction, right around the test mass.
This design will allow to know preciselly the centre of mass and to adjust it. But above all, any permanent offset will be cancelled, as it will pull at times toward the Sun, at times opposite to the Sun. So we can really maintain the test mass free of spurious gravitationnal effects from the probe itself.
Such a probe would be relatively light wheight, so that it could be launched on an interstellar trajectory directly from the surface of the Earth, without using gravitationnal assistance. So it could bring results after only a few years. Otherwise we can use Jupiter' assistance.
Will this design lead one day to a real experiment?
Interesting idea, and pretty much identical to the concept for the http://lisa.jpl.nasa.gov gravitational wave mission, which would reduce the costs of such a mission considerably if the systems could be reused.
Of cource that would rely on LISA ever geiing off the ground, I wrote a undergraduate report about LISA and that was a long time ago! (~9 years) I can't remember what the planned launch date was back then but I don't think it was more than ten years, today, still ten years (2015)!
James
Posted by: Richard Trigaux Sep 5 2005, 08:57 AM
The LISA observatory project will use three test masses, each with its own shield, to detect gravitationnal waves.
The purpose of the LISA and of a Pioneer effect probe is different: the LISA will have to detect much weaker effects, using laser interferometry, while a Pioneer effect probe can be accurate enough with radio location. The LISA would not be bothered with a permament offset in the results, as it is meant to detect only transcient or periodic effects. But such a permanent offset would mess up a Pionner effect probe, as it studies signals which are constant over years.
For this reason I proposed my rotative shield design to cancel any permanent offset. This cannot be used by LISA. So they are developping a very accurate tracking system: 10 nanometres! Figure that this is better than welding the shield to the test mass with steel rods. Eventually this technology may be better than my rotating design to cancel even permanent offsets. So re-using the LISA technology may save most of the development costs for a Pioneer effect probe.
Posted by: The Messenger Sep 5 2005, 04:28 PM
All of these approaches use assumptions we should not be making. If there is a variation in the permeabiliy of space to mass necessary to explain the phenomena I outlined above, there is almost certainly a corresponding gradient in the speed of light.
This can be demonstrated with the Galileo paradox:
Put Galileo on the Dark side of Mercury, rolling his balls to measure the gravitational constant. Because of the nearby mass of the sun, the balls will roll slower, which would cause Galileo, not knowing about GR, to underestimate the G constant. EXCEPT Galileo's clock is also ticking slower, so the value would be very close to correct.
Watching the experiment from an Earth frame of reference, the balls would appear to roll slower, and a GR space curvature correction must be used to explain the phenomena.
Three things: 1) The same observations can be interpreted as a time or space dilation, depending upon the frame of reference. 2) Performing the experiment on Mercury, Galileo could be completely oblivious to the need for GR to explain the results from Earth. 3) It is relatively simple to transfer both frames of reference to a single coordinate system where the absolute pathlength through a given volume of space varies as a function of mass.
Magueijo eluded to this transformation in Faster Than the Speed of Light, where he found it difficult to prove his theory required a new physical concept; and not just a transformation of GR into a completely compatible coordinate system, where pathlengths and the speed of light vary, not time and space curvature. (I am of the opinion that this mathematic transformation provides a better conceptual bases for GR phenomenon.)
So any attempts to measure unknown or poorly characterized forces must also address an untested assumption in measurement theory: the Speed of light is an absolute constant that is not mass dependent; or more exactly: Current GR perameters correctly compensate for mass-dependant effects upon light.
Again, existing solar probes have tightly constrained any deviations from established GR constraints: Bertotti has used Cassini to constrain unexpected GR variance to a factor of 2.3x10^-5 near the Earth's orbit. Perhaps the best solar constraint on the speed of light is the Pioneer Anomally itself - 8x10^-9m/s^2, but this is only beyond the obital distance of Saturn. (Notice that since we use the two-way speed of light to determine the position of the Pioneer probes, the acceleration of the probes could be away from, rather than towards the sun, as long as it is of the same magnitude as any change in the speed of light.)
Bertotti, B., Iess, L., Tortora, P., “A test of general relativity using radio links with the Cassini spacecraft,” Nature 425, 374-376 (2003).
http://lanl.arxiv.org/PS_cache/gr-qc/pdf/0411/0411082.pdf
Again, much of the science needed to nail down these possible discrepancies can be extracted from the current generation of probes, but only if the experimentors are aware of the unbridled parameters and the need for additional onstraints.
Edited to add:
One more question about LISA - unless and until the current LIGO generation of gravity antenna detect ANY gravitational phenomena, should we be vesting in another experiment? IAOTO the waves do exist, but we may be searching with the wrong kind of antenna.
Posted by: jamescanvin Sep 6 2005, 12:17 AM
Heading off topic but...
QUOTE (The Messenger @ Sep 6 2005, 02:28 AM)
One more question about LISA - unless and until the current LIGO generation of gravity antenna detect ANY gravitational phenomena, should we be vesting in another experiment? IAOTO the waves do exist, but we may be searching with the wrong kind of antenna.
Well LISA will be serching in a completely different frequency band. A band which should include waves from binary neutron stars which pretty much must exists given current observations (and at a known amplitude), unlike LIGO which can only detect much more exotic and theoretical objects and mergers. So yes I do think it's worth investing in, even given the non-detections at LIGO.
Posted by: The Messenger Sep 6 2005, 05:53 AM
QUOTE (jamescanvin @ Sep 5 2005, 05:17 PM)
Heading off topic but...
Well LISA will be serching in a completely different frequency band. ..
Damn! I'll say we need LISA, yesterday, not too many years from now. Any chance of bumping LISA ahead of PLANCK? The CMB has a local contamination issue that needs to be resolved to reathenticate, if possible, the accuracy of the WMAP results.
But A drag-free triangulated laser ranged probe orbiting the Sun will also provide constraints upon Pioneer-like acceleration anomalies
if they effect lasar ranging.
Posted by: Richard Trigaux Sep 6 2005, 06:37 AM
Thanks jamescanvin for the image and the info it contains.
What would be fine is if somebody have the log-log plot, amplitude versus frequency, with expected domain for each gravitationnal wave source, and the expected sensitivity of each instrument.
What I heard (to check) is that the LIGO gravitational wave observatory is curently reaching its full sensitivity, but it still detected nothing (the only thing it could detect, neutron stars spiraling, would happen only once a year in average).
Posted by: jamescanvin Sep 7 2005, 12:27 AM
QUOTE (Richard Trigaux @ Sep 6 2005, 04:37 PM)
What would be fine is if somebody have the log-log plot, amplitude versus frequency, with expected domain for each gravitationnal wave source, and the expected sensitivity of each instrument.
Yes, that was what I was looking for yesterday, but couldn't while rushing round.
Couldn't have been looking very hard as a quick search this morning and, ta-dar!
I think that curve is for Advanced LIGO , Standard LIGO is about one order of magintude less sensitive.
QUOTE (Richard Trigaux @ Sep 6 2005, 04:37 PM)
What I heard (to check) is that the LIGO gravitational wave observatory is curently reaching its full sensitivity, but it still detected nothing (the only thing it could detect, neutron stars spiraling, would happen only once a year in average).
Yes, I don't think we need to start rethinking gravitational wave theory just yet, it's not too surprising that nothing has been detected by LIGO so far. Lets wait for Advanced LIGO first (2009)
James
Posted by: Richard Trigaux Sep 7 2005, 05:42 AM
QUOTE (jamescanvin @ Sep 7 2005, 12:27 AM)
Yes, that was what I was looking for yesterday, but couldn't while rushing round.
Couldn't have been looking very hard as a quick search this morning and, ta-dar!
James
Thanks very much James it is exactly what I wished!!! This graphics tells us exactly what we can expect or not!!
QUOTE (jamescanvin @ Sep 7 2005, 12:27 AM)
I think that curve is for Advanced LIGO , Standard LIGO is about one order of magintude less sensitive.
Yes, I don't think we need to start rethinking gravitational wave theory just yet, it's not too surprising that nothing has been detected by LIGO so far. Lets wait for Advanced LIGO first (2009)
James
Yes, no need yet to rethink the gravitationnal wave theory, as LIGO today is only able to detect rare events, mainly neutron stars and black hole coalescence, and only the stronger.
Black holes coalescence is, I think, something very well understood (in the context of General realtivity. But even without relativity we can expect that star-sized masses spiraling a high speed will produce strong gravitationnal effects.). Neutron star coalescence and super nova core collapse are slightly less understood (especially SN core coalescence may be highly disordered and unsymmetrical) but the theory is still reliable. So it is expectable that we detect some events before 2009, and only some years after this date, if we detect nothing, the gravitationnal wave theory is at risk.
Posted by: dvandorn Sep 7 2005, 07:36 AM
Once again, I'm asking a question that I probably ought to just Google up for myself, but it does go along with the thread...
One of the experiments in the Apollo 17 ALSEP was the Lunar Surface Gravimeter. As I recall, it was designed to detect gravity waves. (It failed because it was balanced in 1G and was entirely out of balance, and hence useless, in 1/6G.)
Does anyone know what types of waves the LSG was designed to detect? Would it have been more in the LISA range or the LIGO range?
I guess I'm wondering what kinds of things we might have been gathering data on for more than 30 years if the instrument had just been designed properly...
-the other Doug
Posted by: edstrick Sep 7 2005, 08:22 AM
I'd have to check, but I think the Apollo 17 instrument's name included the term "Tidal". They were looking at freequencies below those the seismometer would detect, at least in part... looking for whole-moon "ringing" frequencies, like the ringing of the whole earth after a Richter 8+ quake.
The instrument failed because it was balanced in 1 G with the aid of a loading mass or spring which was unloaded on the moon. The problem was an arithmetic booboo in the calculation of the design for lunar gravity.. the instrument had a "bias" range that was adjustable for a range of lunar gravities, or really more accurately, for a range of instrument sensitivities... The adjustable range of the instrument was such that actual lunar gravity (very well known) was outside the adjustment range. This is similar to the focus failure on Deep Impact's hi rez camera.. The camera was "focussed" from pre-launch out of focus conditions by heating the carbon-composite truss to drive out water vapor in vaccuum, intending to slow down and stop when the instrument approached and achieved perfect focus..... it never got there due to a ground base calibration problem. The actual focus point was outside of the adjustment range.
Posted by: Bob Shaw Sep 7 2005, 09:42 AM
QUOTE (edstrick @ Sep 7 2005, 09:22 AM)
The instrument failed because it was balanced in 1 G with the aid of a loading mass or spring which was unloaded on the moon. The problem was an arithmetic booboo in the calculation of the design for lunar gravity.. the instrument had a "bias" range that was adjustable for a range of lunar gravities, or really more accurately, for a range of instrument sensitivities... The adjustable range of the instrument was such that actual lunar gravity (very well known) was outside the adjustment range. This is similar to the focus failure on Deep Impact's hi rez camera.. The camera was "focussed" from pre-launch out of focus conditions by heating the carbon-composite truss to drive out water vapor in vaccuum, intending to slow down and stop when the instrument approached and achieved perfect focus..... it never got there due to a ground base calibration problem. The actual focus point was outside of the adjustment range.
Oooh, dear! Don't let a certain scientist-astronaut know, this may have wasted some of that precious EVA time during which rocks could have been examined. I can just imagine a series of unexplained murders, with the victims attended to with a balance spring tied between a gnomon and a lunar rake...
Posted by: Richard Trigaux Sep 7 2005, 10:28 AM
QUOTE (dvandorn @ Sep 7 2005, 07:36 AM)
Does anyone know what types of waves the LSG was designed to detect? Would it have been more in the LISA range or the LIGO range?
I guess I'm wondering what kinds of things we might have been gathering data on for more than 30 years if the instrument had just been designed properly...
-the other Doug
I think that, even if such an instrument was properly designed, it had far from enough sensitivity to detect expected gravitationnal waves. Gravimeters are very sensitive indeed, they can detect such "low" masses as mountains, and even less (remember the historical Cavendish experiment which measured the effect of a some kilograms mass). But this is very far from enough to detect gravitationnal waves, which are many orders of magnitude under this level of sensitivity. Otherwise it would not be necessary to build such complicated experiments as LIGO, it would be enough to send a gravimeter in the ISS.
Perhaps the most powerfull recent gravitationnal event was the supernova in 1978, but who knows what happens in the gravitationnal field.
Posted by: edstrick Sep 7 2005, 10:38 AM
When the gravimeter was proposed, selected and designed, the PI (Weber, I think) was claiming or about to claim possible detections of grativational waves with ultrasensative suspended cylinders. The consensus then and now was that plausible sources of waves in the frequency range that the sensors could detect were many orders of magnitude too small to detect (at least at distances out where there was any chance of an event occurring). But theory in 1970 was much less precise than now, too. By observing natural tidal oscillations of the moon and very low frequency seismic signals, they hoped to have a valuable experimet regardless of whether the "blue sky" gravity wave search was a bust or not.
Posted by: Richard Trigaux Sep 7 2005, 02:38 PM
QUOTE (edstrick @ Sep 7 2005, 10:38 AM)
When the gravimeter was proposed, selected and designed, the PI (Weber, I think) was claiming or about to claim possible detections of grativational waves with ultrasensative suspended cylinders. The consensus then and now was that plausible sources of waves in the frequency range that the sensors could detect were many orders of magnitude too small to detect (at least at distances out where there was any chance of an event occurring). But theory in 1970 was much less precise than now, too. By observing natural tidal oscillations of the moon and very low frequency seismic signals, they hoped to have a valuable experimet regardless of whether the "blue sky" gravity wave search was a bust or not.
Yes I remember that there was hopes to find gravitationnal waves with large aluminium cylinders which may resonate and amplify the wave signal. The first experiments to find gravitationnal waves started with such detectors, but they never produced anything. But the search was open...
Posted by: dvandorn Sep 7 2005, 06:33 PM
QUOTE (Bob Shaw @ Sep 7 2005, 04:42 AM)
Oooh, dear! Don't let a certain scientist-astronaut know, this may have wasted some of that precious EVA time during which rocks could have been examined. I can just imagine a series of unexplained murders, with the victims attended to with a balance spring tied between a gnomon and a lunar rake...
Oh, that particular scientist-astronaut was well aware of the problem -- for one thing, when the PI found his instrument wouldn't uncage, he *insisted* that this particular scientist-astronaut must have deployed it improperly, must not have leveled it right. So Houston told him to go back and re-level the experiment -- three times. When told it would not uncage, Schmitt even kicked it, hard, and then re-leveled it again. It still did not uncage.
Schmitt was, indeed, *quite* angry that such a screw-up had cost precious lunar surface EVA time.
From what I understand, though, even with the main beam caged, the LSG actexd as a fair one-axis seismometer...
-the other Doug
Posted by: dvandorn Sep 7 2005, 06:41 PM
QUOTE (edstrick @ Sep 7 2005, 03:22 AM)
I'd have to check, but I think the Apollo 17 instrument's name included the term "Tidal".
Not in the experiment title, no -- Apollo 17 carried two gravimeters, the Lunar Surface Gravimeter (LSG) and the Lunar Portable Gravimeter (LPG). The tidal reference may have been in the detailed description of the LSG, but it was not part of the instrument's name.
The LPG was the same type of instrument used by oil companies to find salt domes underneath otherwise flat land -- oil and gas are often entrained in salt domes. It detected negative anomalies on the slopes of the massifs and positive anomalies on the valley floor, indicating just how much more massive the basaltic valley fill is when compared to the massifs. IIRC, the anomalies were on the order of 10 to 30 milligals.
So, the LSG was an ultra-sensitive seismometer that hoped to use the entire mass of the Moon to detect gravity waves? Interesting... even if we now think that gravity waves would have been undetectable with such an instrument.
-the other Doug
Posted by: Bob Shaw Sep 7 2005, 08:47 PM
QUOTE (dvandorn @ Sep 7 2005, 07:33 PM)
Oh, that particular scientist-astronaut was well aware of the problem -- for one thing, when the PI found his instrument wouldn't uncage, he *insisted* that this particular scientist-astronaut must have deployed it improperly, must not have leveled it right. So Houston told him to go back and re-level the experiment -- three times. When told it would not uncage, Schmitt even kicked it, hard, and then re-leveled it again. It still did not uncage.
Schmitt was, indeed, *quite* angry that such a screw-up had cost precious lunar surface EVA time.
From what I understand, though, even with the main beam caged, the LSG actexd as a fair one-axis seismometer...
-the other Doug
other Doug:
Was the PI's body ever found?
Bob Shaw
Posted by: edstrick Sep 8 2005, 10:49 AM
"From what I understand, though, even with the main beam caged, the LSG actexd as a fair one-axis seismometer...
-the other Doug"
As far as I know there were no science results whatever published from the instrument in that mode. I think the sensativity was far too low for any signal other than astronauts stomping by.
Posted by: The Messenger Sep 8 2005, 06:21 PM
QUOTE (Richard Trigaux @ Sep 7 2005, 03:28 AM)
...
Perhaps the most powerfull recent gravitationnal event was the supernova in 1978, but who knows what happens in the gravitationnal field.
The failure to observe any evidence of SN1987A by any gravity wave detectors is not a good omen. True, the GW spectrum of a supernova is up-in-the-air, but an explosion of that magnitude, that close, should have created enough broad spectrum transients we should have found something, especially since the timing of the event is well known.
I wouldn't pin my life's savings on Advanced LIGO - which seems to be progressing slightly ahead of schedule. Every generation of gravity wave detectors from Weber's work in the '70's on, have been built with the expectation that a GW event was just one pixal below the horizon.
Advanced LIGO:
http://www.ligo.caltech.edu/docs/G/G050364-00.pdf
QUOTE
Eventually, with 1-year of data at design sensitivity, the LIGO detectors will be sensitive at a level several times below the nucleosynthesis bound.
http://arxiv.org/PS_cache/astro-ph/pdf/0507/0507254.pdf
FWI worth, there is still a great deal of contraversy in the supernova community about just what the gamma rays, and expansion RINGs associated with 1987A mean. John Middleditch amoung others, is convinced both the rings and rays reveal a binary event, and he argues most supernovae involve binary systems. This grates against SN Ia theory, but his arguments, (including the 'double humped' light curves observed in many SN Ia spectra.) are strong.
http://arxiv.org/abs/astro-ph/0310671
http://arxiv.org/abs/astro-ph/0311484
Posted by: Richard Trigaux Sep 9 2005, 07:21 AM
QUOTE (The Messenger @ Sep 8 2005, 06:21 PM)
I wouldn't pin my life's savings on Advanced LIGO - which seems to be progressing slightly ahead of schedule. Every generation of gravity wave detectors from Weber's work in the '70's on, have been built with the expectation that a GW event was just one pixal below the horizon.
Advanced LIGO:
http://www.ligo.caltech.edu/docs/G/G050364-00.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0507/0507254.pdf
Very interesting article, although arduous to read. To summarize, the purpose of LIGO is to detect the cosmic background gravitationnal noise caused by very early cosmological events, far before the electromagnetic background. Today LIGO has not yet achieved this goal, but it made only short runs of data sampling which were rather aimed at improving sensitivity and eliminating instrument noise. With a long run at expected maximum sensitivity they expect to detect the level of gravitationnal waves predicted by the most recent theories of inflation. If they really achieve this design sensitivity and still not fing a gravitationnal background noise, the theories of inflation are at risk. Still only some years of work to let us know...
QUOTE (The Messenger @ Sep 8 2005, 06:21 PM)
Every generation of gravity wave detectors from Weber's work in the '70's on, have been built with the expectation that a GW event was just one pixal below the horizon.
This is often like this in difficult scientifical achievements. Look for instance at the tokamac, the quantum computer, superconduction at ambient temperature... This is also due to the fact that the first researchers were really optimistic. Today evaluations of gravitationnal waves are, alas, much more pessimistic, and if they were know in 1970 Weber would not have started his experiment. Weber simply did what was best possible to do at his epoch, knowing what we knew.
QUOTE (The Messenger @ Sep 8 2005, 06:21 PM)
FWI worth, there is still a great deal of contraversy in the supernova community about just what the gamma rays, and expansion RINGs associated with 1987A mean.
Please remember that the curious set of three non-coplanar rings around SN1987A were already here before the explosion. They were discovered after, with close examination of the place, but such rings are more likely of the planetary nebula family. It was said at this epoch that there will be new hubbub here when the expanding fireball would reach the first ring, 20 years later (2007). Also we are still to detect the predicted blinking of the central object indicating the presence of a pulsar.
Posted by: edstrick Sep 9 2005, 07:45 AM
It has been hoped that cosmic sources of gravitational radiation (as opposed to supernovae and massive object collissions) are stronger than predicted, or that there's unpredicted sources that have relatively frequent events strong enough for the first generation LIGO detection systems, but basically nobody expects it. Detectors have gotten much better than Weber's original cylinders, but my impression is that expectations of predicted source strength-frequency combinations have been such that no detector so far has been expected to detect anything by the general gravitational wave community. LIGI, I believe, works at much too high a frequency for detecting big bang related radiation and the like.
As far as SN1987A goes, we're detecting the blast wave interacting with the inner edge of a lumpy ring which is progressively lighting up as the blast expands. There is still no trace of either a black hole or neutron star in the supernova remenant inside the ring, or of energy being emitted from one. Some models in the past have suggested that in some cases there may be nothing left, but those I think are in disrepute, so the non-observation of a massive object is "A Puzzlement"
Posted by: Richard Trigaux Sep 9 2005, 08:17 AM
QUOTE (edstrick @ Sep 9 2005, 07:45 AM)
As far as SN1987A goes, we're detecting the blast wave interacting with the inner edge of a lumpy ring which is progressively lighting up as the blast expands. There is still no trace of either a black hole or neutron star in the supernova remenant inside the ring, or of energy being emitted from one.
Thanks for the info, edstrick. The lumpy ring you speak about is the innermost of the three rings, the one which is coplanar with the star.
QUOTE (edstrick @ Sep 9 2005, 07:45 AM)
Some models in the past have suggested that in some cases there may be nothing left, but those I think are in disrepute, so the non-observation of a massive object is "A Puzzlement"
Yes there are some models predicting a nuclear explosion of the star, without gravitationnal collapse. In this case all the mass is blasted away and nothing remains in the centre. But this is for peculiar cases of binary stars, I do not think it fits for SN1987A, which is believed to be basically a gravitationnal collapse of a massive star which exhausted all its nuclear power. But the process leading from a star to a neutron star or black hole is not yet understood. The only thing sure is that there was a blast of neutrinos detected, indicating very high temperatures reached in the core. But we do not know if a black hole or a neutron star was created. By the way this star was not very massive, it could have given only a white dwarf (an idea of mine, without any waranty). I remember that the detection of a blinking light was expected 10 years after. Now 18 years passed by...
Posted by: The Messenger Sep 12 2005, 01:49 PM
QUOTE (Richard Trigaux @ Sep 9 2005, 12:21 AM)
Please remember that the curious set of three non-coplanar rings around SN1987A were already here before the explosion. They were discovered after, with close examination of the place, but such rings are more likely of the planetary nebula family. It was said at this epoch that there will be new hubbub here when the expanding fireball would reach the first ring, 20 years later (2007). Also we are still to detect the predicted blinking of the central object indicating the presence of a pulsar.
News to me - can you provide a source? Middleditch based his models on fast rotating binary systems, and the resulting Gamma Rays, so I don't think prior rings cause a conundrum (prior rings being a product of the orbital dog-and-cat fight (?)).
Posted by: Richard Trigaux Sep 12 2005, 02:23 PM
QUOTE (The Messenger @ Sep 12 2005, 01:49 PM)
News to me - can you provide a source? Middleditch based his models on fast rotating binary systems, and the resulting Gamma Rays, so I don't think prior rings cause a conundrum (prior rings being a product of the orbital dog-and-cat fight (?)).
This set of three non-coplanar rings was photographied just after the blast was extinct, some months after the supernova, when astronomers began to examine the place. I remember well that it was in all the science reviews (Here in France "Science et Avenir", "Science et Vie", "Pour la science" , and also in amateur astronomy reviews. At that time the fireball from the explosion was just an unresolved point at the centre of the well resolved three rings. Previous photos of the same place showed the parent star, but were not large enough to show the rings. These rings much puzzled the astronomers, and they played a role in the planetary nebula theory (since it was found one or several planetary nebula looking like hour glasses, ressembling the rings of 1987A). They are now expected to form from binary systems. But I never heard of a companion star of SN1987A, with my opinion if it exists it must be a very weak star, white dwarf, neutron star or black hole. Anyway it puzzles me that today some people (and even scientists) seem to think that the three rings resulted from the explosion. Today the fireball of the explosion is just catching the innermost ring.
Another curious thing is that, while the fireball was still very bright, days of weeks after the explosion,I heard mentioned that just nearby there was a huge transcient infrared source, most powerfull than the entire Magellanic cloud. But I never heard of this again, perhaps it was just an observation error. Often unexplained facts are considered as mistakes and forgotten. But there may be some new thing about. Today people may think that it was the effect of a focused gamma ray beam like those predicted by some supernova theories.
Sorry, I have no other sources than my memories of the scientific press at this epoch. If you want more precise sources, I think you should look in the archives of science and astronomy reviews (like the "scientific American" in the months following the supernova, I think you cannot miss the images of the three rings.
Posted by: The Messenger Sep 12 2005, 06:56 PM
QUOTE (Richard Trigaux @ Sep 12 2005, 07:23 AM)
But I never heard of a companion star of SN1987A, with my opinion if it exists it must be a very weak star, white dwarf, neutron star or black hole. Anyway it puzzles me that today some people (and even scientists) seem to think that the three rings resulted from the explosion. Today the fireball of the explosion is just catching the innermost ring.
Thanks -
Nisenson argues the 'spots' are indeed likely supernova remnants, but I am not sure if he is arguing the rings are actual remnants or "spotlighted" illuminations of existing nebula.
http://arxiv.org/abs/astro-ph/9904109
You are correct in stating a companion star for 1987A has never been discovered. The column of energy released was so enormous, Middleditch speculates a high volume of the star may have undergone 'unidirectional weak interactions'. A relativistic laser(?)
I was looking for a mechanism to explain the relativistic accelerations Nisenson is trying to interpret, when I stumbled across the possibly 'non-Newtonian' trend in the solar system I outlined above. FWIW, I haven't convinced anyone in the field this could be a real aspect of gravity, but I haven't found anyone who's eyes don't glaze over the second they realize the implications, either.
Posted by: Richard Trigaux Sep 13 2005, 10:15 AM
QUOTE (The Messenger @ Sep 12 2005, 06:56 PM)
You are correct in stating a companion star for 1987A has never been discovered.
Such a companion is deemed necessary to explain the existence of the rings (some planetary nebulae geometries are suposed to appear in binary systems). Alas we don not have precise spectra of 1987A before the explosion (it was just a blue spot among thousands of others). To explain the "disappearance" of the companion, we can suppose:
-it is very weak (white dwarf, neutron star, black hole. But I think we cannot expect the presence of a white dwarf as a companion to a large star)
-it was blasted away during the explosion
-it was absorbed some thousands years ago when 1987A was a red giant, just after involving in the rings. Eventually such three-ring geometry would be the signature of this kind of event.
Remember also that a blue star exploding as a supernova was a surprise; astronomers were thinking of SN1987A as being an ordinary blue star on its main sequence, not the likely candidate for a supernova. (It was the first time the star forming the supernova was known). The generaly retained explanation is that 1987A had undergone a red giant stage earlier, but since some thousand years it had subsided into a smaller blue star. Such variations in near-death stars are expected by theories and supported by observations.
Posted by: ljk4-1 Sep 13 2005, 01:17 PM
QUOTE (Richard Trigaux @ Sep 13 2005, 05:15 AM)
Such a companion is deemed necessary to explain the existence of the rings (some planetary nebulae geometries are suposed to appear in binary systems). Alas we don not have precise spectra of 1987A before the explosion (it was just a blue spot among thousands of others). To explain the "disappearance" of the companion, we can suppose:
-it is very weak (white dwarf, neutron star, black hole. But I think we cannot expect the presence of a white dwarf as a companion to a large star)
-it was blasted away during the explosion
-it was absorbed some thousands years ago when 1987A was a red giant, just after involving in the rings. Eventually such three-ring geometry would be the signature of this kind of event.
Remember also that a blue star exploding as a supernova was a surprise; astronomers were thinking of SN1987A as being an ordinary blue star on its main sequence, not the likely candidate for a supernova. (It was the first time the star forming the supernova was known). The generaly retained explanation is that 1987A had undergone a red giant stage earlier, but since some thousand years it had subsided into a smaller blue star. Such variations in near-death stars are expected by theories and supported by observations.
Perhaps it was an industrial accident.
From the article "Detectability of Extraterrestrial Technological Activities"
by Guillermo A. Lemarchand:
http://www.coseti.org/lemarch1.htm
FIGURE 2: Concept of an "artificial" blue straggler star according to Reeves (1985). In this figure, a series of hydrogen bombs or powerful laser beams are aimed at the surface of a star, creating a "hot point" and rejuvenating the unused hydrogen, thus keeping the star on the Main Sequence for a longer period of time than would be natural.
http://www.coseti.org/images/lefig_2.gif
Reeves (1985) speculated on the origin of mysterious stars called blue stragglers. This class of star was first identified by Sandage (1952). Since that time, no clear consensus upon their origins has emerged. This is not, however, due to a paucity of theoretical models being devised. Indeed, a wealth of explanations have been presented to explain the origins of this star class. The essential characteristic of the blue stragglers is that they lie on, or near, the Main Sequence, but at surface temperatures and luminosities higher than those stars which define the cluster turnoff. A review of current thinking about these stars in the light of recent visible and ultraviolet Hubble Space Telescope observations assigns an explanation to stellar mergers occurring in the dense stellar environment of globular clusters (Bailyn, 1994).
Reeves (1985) suggested the intervention of the inhabitants that depend on these stars for light and heat. According to Reeves, these inhabitants could have found a way of keeping the stellar cores well-mixed with hydrogen, thus delaying the Main Sequence turn-off and the ultimately destructive, red giant phase.
Beech (1990) made a more detailed analysis of Reeves' hypothesis and suggested an interesting list of mechanisms for mixing envelope material into the core of the star. Some of them are as follows:
* Creating a "hot spot" between the stellar core and surface through the detonation of a series of hydrogen bombs. This process may alternately be achieved by aiming "a powerful, extremely concentrated laser beam" at the stellar surface.
* Enhanced stellar rotation and/or enhanced magnetic fields. Abt (1985) suggested from his studies of blue stragglers that meridional mixing in rapidly rotating stars may enhance their Main Sequence lifetime.
If some of these processes can be achieved, the Main Sequence lifetime may be greatly extended by factors of ten or more. It is far too early to establish, however, whether all the blue stragglers are the result of astroengineering activities.
Posted by: The Messenger Sep 13 2005, 04:16 PM
Suggestions, by anyone, of engineering on this scale, is not productive and not scientifically motivated.
Posted by: Richard Trigaux Sep 13 2005, 06:06 PM
QUOTE (The Messenger @ Sep 13 2005, 04:16 PM)
Suggestions, by anyone, of engineering on this scale, is not productive and not scientifically motivated.
I mostly agree with you, but...
Imagine a million years old civilization, with technologies such as self-reproducing machines, fusion energy, etc... and plenty of time. Soon within reach of us.
Unless such a civilisation turns more ethical/spiritual than technological, there is no limit with such a technology, and it is not impossible we discover stars and even galaxies which were engineered over millions (or billions) of years. Simply we have not yet evidences (and even not suspicion) of it. There is alway this temptation when we discover something we do not understand: and if it was artificial? Remember the first pulsars: their extreme accuracy was not yet understood, and many scientists seriously considered they could be some interstellar beacons...
Coalescence of stars are a sufficient explanation for blue stragglers. A catastrophe which could happpen in some years, projecting all their planets (inhabited?) into blaze or into the darkness of space. Living into a dense star cluster may offer aver beautiful night sky, but it is also a ver dangerous place where most plants are ejected from their orbit by star encounters. so it is not the most likely place to find evolved life.
Posted by: The Messenger Sep 14 2005, 03:31 PM
Returning to the Pioneer Anomally:
You may or may not be aware of the curious brightening phenomenon being studied by Ann Verbiscer, per the Planetary Weblog:
QUOTE (Emily L)
"We see three different views of Saturn on different dates. The globe of Saturn hardly looks different at all at these small differences in phase angle. But look at the rings! With the minutest difference in phase angle -- from 0.13 degrees down to 0.02 degrees -- the rings suddenly flash into brilliant light. Anne told me that she saw similar effects on Saturn's icy satellites, especially Enceladus. The size of the opposition surge she saw was "drastically higher, 40% higher, than previously published values."
I'm not an astronomical observer myself so Anne had to explain to me what causes the opposition surge. One explanation is "shadow hiding" -- at any non-zero phase angle, the particles in the rings cast shadows across other particles in the rings, so that darkens the surface. But at zero phase, you see no shadows at all, and the surface looks brighter. But Anne said that "it doesn't work" to explain all of the observed opposition effect. You need something more, like coherent backscatter: that is, constructive interference of the light being reflected from the rings and Enceladus.
There is an explanation that is consistent, actually a necessary constraint, upon the permeability hypothesis I entered above:
The rings of Saturn, the highly reflective surfaces of some of the moons, are more like mirrors than nominal planetary surfaces. The sunlight reflected by the rings, therefore, more closely resembles a mirrored reflection of the sun, and will return a loosely coherant image of the sun.
When the Earth passes exactly between the Sun and Saturn, the rings and more reflective moons brighten. Why would the reflection be brighter at the very center?
If and ony if there is curvature of space. The image of the sun is focused only at the center, at anyother position of the Earth relative to the sun and Saturn, the image is deconvoluted.
When the Earth is exactly positioned in front of the sun, a perfectly curved lens would return a much brighter reflection of the sun. That is exactly what is happening.
And why would there be curvature? If and only if the permeability of space varies, increasing the speed of light with increasing distance from the center of the solar system, and this would be true if and only if the permeability of space is a function of MASS.
OK, There may be other solutions: Fressnel lensing, for example, but the solution is a lensing solution because the amount of brightening is also a function of wavelength, as would be expected with any single density lensing element.
The curvature has to be very slight...almost undetectable, but not quite, because it produces this brilliant mirror effect exactly in the center - just as a gravitational lens should. But the Earth is too far from the sun to experience this kind of curvature, with GR, as formulated by Einstein, to be the cause. (Also the mass of the Earth is not great enough to cause a GR bending of the light.)
This also explains why there are so many 'Gravitational' lenses, and 'micro quasar' lenses in the galaxy: There is a not-so-new physical principle being manifest: The permeability of space is a function of mass, the speed of light is only a constant in an ideal vacuum that includes the absence of any matter.
Returning to the Pioneer Accelerations, they are an artifact: We use the two-way time and speed of light to determine the distance to the probes. As the speed of light increases at a rate of ~1X10^-9m/s^2, the time it takes light to reach the probes and return is less than if the speed of light were constant. We interpret this as an acceleration of the probes towards the sun,
when it is actually a slight acceleration of light away from the sun. (Of course both the speed of light, and the acceleration of the probes are not independently constrained at this time, so the true acceleration of the probes is unknown.)
Posted by: Richard Trigaux Sep 14 2005, 03:46 PM
Messenger, yes the Earth does have a "gravitationnal lens" effect, but it can significantly concentrates light only at a distance of several thousand light-years. This was put at work in the search of "machos" (massive objects such as blue dwarf stars, planets, brown dwarfs, black holes... explaining the dark matter around the galaxy). But the "machos" detected were very far, for instance in the Magellanic cloud, and the most common mass was around half what of the Sun, much larger than Earth. So I think the effect of gravitationnal lens is undetectable from Saturn. The opposition effect is well explained in terms of shadow hiding and back reflection from ice crystals, an effect we can also see on earth clouds (from above). The best evidence is that it was also photographied by Cassini (see somewhere on Cassini site or on this site) and from here it appears as a bright spot on the rings.
Posted by: ljk4-1 Oct 3 2005, 04:46 AM
http://www.issi.unibe.ch/teams/Pioneer/
The Pioneer Explorer Collaboration
Investigation of the Pioneer Anomaly at ISSI
First Team Meeting at ISSI in Bern, Switzerland
November 7-11, 2005
Focus: the Pioneer anomaly
To date, the Pioneer 10 and 11 spacecraft are the most precisely navigated deep-space vehicles. However, as indicated by their radio-metric data, the Pioneers’ orbit reconstructions were limited by a small, anomalous, constant, blue-shifted, Doppler frequency drift of approximately 6 x 10^-9 Hz/s. The drift can be interpreted as due to a constant sunward acceleration of a_P = (8.74 ± 1.33) 10^-10 m/s^2. This interpretation has become known as the Pioneer anomaly.
Although the most obvious explanation would be that there is a systematic origin to the effect, the limited set of the analyzed data does not support any of the suggested mechanisms. We assert that analysis of the entire existing Pioneer data is vital to understanding the anomaly and, hopefully, to finding its origin. Indeed, analysis of the entire existing Pioneer data record is critical in attacking the anomaly on two fronts: (i) an analysis of the early, not rigorously analyzed, data could yield a more accurate direction of the anomaly and hence might help to determine its origin; (ii) by using the entire data set, from 1972 to 2002, one could study the temporal evolution of the anomaly and determine if it is due to on-board nuclear fuel inventory and related heat radiation or other mechanism.
Goal: analysis of the entire Pioneer 10/11 data record
The limited data analyzed previously allowed the detection of the anomaly in the Pioneer data, but not a determination of its origin. With new knowledge of all on-board processes and a diverse team, we propose a two-step process in understanding the origin of the anomaly, namely: (i) analysis of the entire set of existing Pioneer 10 and 11 data, obtained from first launch to the last telemetry received from Pioneer 10, on 27 April 2002, when it was at a heliocentric distance of 80 AU. This data could yield critical new information about the anomaly. If the signal is confirmed and is not due to an on-board systematic, (ii) we will use our new knowledge to develop an instrumental package that will be capable to provide an independent confirmation of the anomaly. We will also study a design for a dedicated mission to explore the anomalous behavior of the Pioneer spacecraft.
Significance: finding the origin of the Pioneer anomaly
This ISSI investigation could lead to a determination of the origin of the anomaly and to a characterization of its physical properties. The proposed investigation is scientifically important, it is timely, and is well situated in Europe. The investigation would be an excellent example to demonstrate the value of interdisciplinary teams in addressing complex problems in fundamental physics and in application of new technologies in spacecraft and mission designs. The results of this study could find their way into many other areas of space-exploration applications in the near future. The most important outcome of this study will be the understanding of the Pioneer anomaly.
http://www.issi.unibe.ch/teams/Pioneer/
Posted by: edstrick Oct 3 2005, 07:15 AM
ljk4-1: "...The Pioneer Explorer Collaboration -- Investigation of the Pioneer Anomaly at ISSI.."
I totally concur with the proposed analysis. We have an "anomaly". Not an "Anomaly" or an "ANOMALY" (if you get what I mean...).
We have an APPARENT force acting on the spacecraft. The best modelling has been unable to explain this anomaly in terms of systematic internally generated forces on the spacecraft, or known, modelable external forces acting on the spacecraft. We now need to extract the most information possible from the mission's data to see how the force varies with 1.) mission phase, 2.) radial location in solar system, and 3.) azimuth/inclination in solar system.
For example, if a reanalysis shows no anomalous acceleration before Jupiter flyby and identical accelerations afterwards... that would suggest an effect arising in an unknown effect on the spacecraft of the Jovian system environment..... particularly the extreme radiation environment.
For another example...Pioneer 11 flew "across" the solar system in a significantly inclined orbit between the Jupiter encounter and it's Saturn encounter, getting a foretaste of out-of-ecliptic science before Ulysses. If a reanalysis shows a force varying with inclination or angle around the sun in the ecliptic and then a relatively constant force after Saturn flyby puts Pioneer 11 on an escape trajectory...... Hmmmmmm.....!
Posted by: Richard Trigaux Oct 3 2005, 08:15 AM
Thanks ljk4-1 for your interesting contribution. And edstrick too
To analyse the existing set of data is obviously the first thing to do before building a space probe to investigate a gaz leak on Pioneer.
-Is the effect real?
-Is it constant, or depending on distance, attitude, fuel aging, direction, planet neighbouring, distance from the ecliptic?
All this would give us clues about its nature: gravitation, electromagnetic, solar wind, local reaction...
By the way it is said that the computers able to read the Pioneer data are to be scraped by the NASA. The first thing to do is obviously to save the data on modern supports. New domain for archaeology: rumaging in old computers magnetic bands.
edstrick, I never heard that the word "anomaly" bears a capital letter, in any of its uses. The Pioneer anomaly may have a very extraordinary explanation, for instance that the probe was followed by a spaceship from another civilization, or that it was used by yogis to demonstrate their supernatural powers. Simply such kind of explanations can be envisioned only after all the other explanations failed. More likely the Pioneer anomaly bears the possibility of some fundamental discovery in physics or in astronomy, so it is worth the study. But there are many chances that we simply find a gaz leak, thruster malfunction or something trite in this style.
But of course I did not missed your point about ANOMALIES! I am no more interested than you by people who spread false informations and false theories: they only muddle things. If there is somewhere something really unexplained, they may rather spoil the discovery than encourage its study.
Posted by: deglr6328 Oct 3 2005, 09:53 AM
sooooo did the planetary soc. get the data or what...? They haven't updated on us the status of thier original $250K begathon since like March.
Posted by: edstrick Oct 3 2005, 09:57 AM
<grin> by "anomaly" I mean an ordinary scientific/engineering unexplained datum due to inadequate modeling, systematic error in measurements, etc.... like the false indications that there was a 10'th planet making Neptune "wander", triggering the search that found Pluto.
An "Anomaly" (tone of voice emphasis implied) would be something that really starts to look like it suggests new astronomy, new physics.... something that is well defined enough and stubborn enough after sustained efforts to make it go away, that people (not just the arm-waving fringe) start to work hard on resolving it. The solar neutrion flux anomaly was one... solved by the confirmation that solar neutrinos change type en-route from the sun, so we only detect 1/3 of them with the original detectors.
And of course ANOMALY (capslock, funny font, guy with tin hat handing out mimeographed treatises to anybody he can buttonhole at a scientific meeting) is what the Hoaxland crowd assume it's most likely to be. (eyeballs rolled expression).
Posted by: Richard Trigaux Oct 3 2005, 12:40 PM
QUOTE (edstrick @ Oct 3 2005, 09:57 AM)
<grin> by "anomaly" I mean an ordinary scientific/engineering unexplained datum due to inadequate modeling, systematic error in measurements, etc.... like the false indications that there was a 10'th planet making Neptune "wander", triggering the search that found Pluto.
An "Anomaly" (tone of voice emphasis implied) would be something that really starts to look like it suggests new astronomy, new physics.... something that is well defined enough and stubborn enough after sustained efforts to make it go away, that people (not just the arm-waving fringe) start to work hard on resolving it. The solar neutrion flux anomaly was one... solved by the confirmation that solar neutrinos change type en-route from the sun, so we only detect 1/3 of them with the original detectors.
And of course ANOMALY (capslock, funny font, guy with tin hat handing out mimeographed treatises to anybody he can buttonhole at a scientific meeting) is what the Hoaxland crowd assume it's most likely to be. (eyeballs rolled expression).
Thank you for the nuances. The Pioneer anomaly if likely of the first kind (anomaly) but there is enough chance it is of the seconc kind (Anomaly) so that it is worth studying it (and re-examining the whole data set is definitively the best to start with).
By the way, the custom of wearing tin-hats comes from the idea that naughty aliens influence us by telepathy. But if telepathy exists, it is likely not an electromagnetic phenomenon, so the tin hat is of no use.
Posted by: edstrick Oct 4 2005, 06:27 AM
Aliens?... I thought it was the CIA and FBI.... or maybe they are space aliens here to control us!
NATIONAL OUTQUIRER
(Picture of Michael Jackson, Elizabeth Taylor, and H. Ross Perot)
Headline: CELEBRITY SPACE ALIENS LIVING AMONG US.
(HRP is obviously a disguised Ferengi... the ears.. the nose.. the money...)
Posted by: Richard Trigaux Oct 4 2005, 07:37 AM
QUOTE (edstrick @ Oct 4 2005, 06:27 AM)
Aliens?... I thought it was the CIA and FBI....
They do not need telepathy for this, they have tele...vision.
There are rumors too of electromagnetic weapons able of having effects of the brain, such as make us hear voices. Far-fetched, but not completelly impossible I think. But if ever there is one day a government pervert enough to use such weapons against its citizens, it will be that the society would have gone very very wrong far before...
Posted by: edstrick Oct 4 2005, 10:51 AM
You know what the problem is with make-believe paranoia?
(looking around suspiciously...)
YOU'RE PROBABLY RIGHT!
Posted by: Richard Trigaux Oct 4 2005, 04:41 PM
QUOTE (edstrick @ Oct 4 2005, 10:51 AM)
You know what the problem is with make-believe paranoia?
(looking around suspiciously...)
YOU'RE PROBABLY RIGHT!
AAAAAARRRGGHH
Posted by: ljk4-1 Oct 4 2005, 07:35 PM
Astrophysics, abstract
astro-ph/0504367
From: Gary Page [view email]
Date (v1): Sun, 17 Apr 2005 17:04:48 GMT (32kb)
Date (revised v2): Sat, 1 Oct 2005 13:46:27 GMT (43kb)
Utilizing Minor Planets to Assess the Gravitational Field in the Outer Solar System
Authors: Gary L. Page, David S. Dixon, John F. Wallin
Categories: astro-ph
Comments: Added substantial new material dealing with ability to observed effects addressed in paper
The twin Pioneer spacecraft have been tracked for over thirty years as they headed out of the solar system. After passing a heliocentric distance of 20 AU, both exhibited a systematic error in their trajectories that can be interpreted as a constant acceleration towards the sun and that has come to be known as the Pioneer Effect.
Spacecraft systematics are its most likely explanation, but there have been no convincing arguments that that is the case. The alternative, that the Pioneer Effect represents a real phenomenon, is very appealing for many reasons. What is lacking is a means of measuring the effect, its variation, its potential anisotropies, and its region of influence.
We show that minor planets provide an observational vehicle for investigating the gravitational field in the outer solar system, and thus provide a means of measuring the Pioneer Effect and potentially to either support or refute its existence as a real phenomenon. Minor planets can be used for this purpose because they have a large mass and are large and bright enough to be observed for useful intervals.
Thus, even if the Pioneer Effect does not represent a new physical phenomenon, minor planets can be used to probe the gravitational field in the outer solar system. Since there are very few intermediate range tests of gravity at the multiple AU distance scale, this is a worthwhile endeavor in its own right. It might even be possible to differentiate between the predictions of alternative explanations for the Pioneer Effect.
http://arxiv.org/abs/astro-ph/0504367
Posted by: ljk4-1 Oct 26 2005, 02:08 PM
Paper: astro-ph/0506281
replaced with revised version Mon, 24 Oct 2005 20:43:50 GMT (41kb)
Title: Analytic Gravitational-Force Calculations for Models of the Kuiper Belt,
with Application to the Pioneer Anomaly
Authors: Michael Martin Nieto
Comments: 11 pages, 8 figures, final corrections for publication
Report-no: LA-UR-05-4414
Journal-ref: Phys. Rev D 72 (2005) 083004
We use analytic techniques to study the gravitational force that would be produced by different Kuiper-Belt mass distributions. In particular, we study the 3-dimensional rings (and wedge) whose densities vary as the inverse of the distance, as a constant, as the inverse-squared of the distance, as well as that which varies according to the Boss-Peale model. These analytic calculations yield physical insight into the physics of the problem. They also verify that physically viable models of this type can produce neither the magnitude nor the constancy of the Pioneer anomaly.
\\ ( http://arXiv.org/abs/astro-ph/0506281 , 41kb)
Posted by: ljk4-1 Nov 9 2005, 04:32 PM
Paper (*cross-listing*): gr-qc/0511026
Date: Sun, 6 Nov 2005 02:40:04 GMT (162kb)
Title: Gravitational solution to the Pioneer 10/11 anomaly
Authors: J. R. Brownstein and J. W. Moffat
Comments: 11 pages, 4 figures, 1 table
\\
A fully relativistic modified gravitational theory including a fifth force
skew symmetric field is fitted to the Pioneer 10/11 anomalous acceleration. The
theory allows for a variation with distance scales of the gravitational
constant G, the fifth force skew symmetric field coupling strength omega and
the mass of the skew symmetric field mu=1/lambda. A fit to the available
anomalous acceleration data for the Pioneer 10/11 spacecraft is obtained for a
phenomenological representation of the "running" constants and values of the
associated parameters are shown to exist that are consistent with fifth force
experimental bounds. The fit to the acceleration data is consistent with all
current satellite, laser ranging and observations for the inner planets.
\\ ( http://arXiv.org/abs/gr-qc/0511026 , 162kb)
Posted by: Myran Nov 9 2005, 09:10 PM
Calculations using the 'MOND' theory (Modified Newtonian dynamics) also have been applied and did fit well with the Pioneer data. No fifth force needed in that case.
Some more on MOND here:
http://www.astro.umd.edu/~ssm/mond/
Posted by: Richard Trigaux Nov 9 2005, 09:21 PM
I wonder if we could do any theory of any kind, adjust parametres and obtain a fit with anything.
But if the fit goes for not only Pioneer data, but all similar data, it is more intersting. Not an evidence of any given theory, but a last of a common mechanism.
Posted by: mike Nov 9 2005, 09:42 PM
That's what a theory is.
Posted by: elakdawalla Nov 10 2005, 01:29 AM
QUOTE (deglr6328 @ Oct 3 2005, 02:53 AM)
sooooo did the planetary soc. get the data or what...? They haven't updated on us the status of thier original $250K begathon since like March.
We've been a little preoccupied!
There are updates on our website here, including reports from a staff member who we sent to the conference in Switzerland:
http://www.planetary.org/programs/projects/pioneer_anomaly/updates.html
And "begathon"...I like it...captures the tone of those four-page letters nicely...
--Emily
Posted by: Myran Nov 10 2005, 05:21 AM
QUOTE
Richard Trigaux said: I wonder if we could do any theory of any kind, adjust parametres and obtain a fit with anything.
But if the fit goes for not only Pioneer data, but all similar data, it is more intersting. Not an evidence of any given theory, but a last of a common mechanism.
Yes, why I was somewhat vary of the idea of a "fifth force" suggested here.
I like things bare bones simple, and so a strong supporter that Occam sharpen his blade.
So when MOND theory originally for explaining the rotation of galaxies also turned out to fit for the much closer Pioneer I happily accepted the notion that there might be something more that makes this idea deserves attention.
(Note: I originally read about the theory in Scientific American, and got interested in it.)
Posted by: lyford Nov 10 2005, 06:41 AM
Call me old fashioned, but I am a bit wary of jettisoning the "old physics" when the effects are at what I understand to be the threshold of detection, and we really don't know what the environment the little guys are swimming in right now is like - we may need to look for a new theory of interstellar wind before altering the laws of motion.
Still it is fun to think about - and it IS possible I suppose -
http://www.planetary.org/programs/projects/pioneer_anomaly/update_20050510b.html from the Planetary Society puts it well:
QUOTE
The simple engineering explanation cannot yet be ruled out, but enough work has been done in trying all the different possibilities that even Occam's Razor allows us to cut a little way into the idea of a new physics.
Posted by: ljk4-1 Nov 10 2005, 02:33 PM
QUOTE (elakdawalla @ Nov 9 2005, 08:29 PM)
We've been a little preoccupied!
There are updates on our website here, including reports from a staff member who we sent to the conference in Switzerland:
http://www.planetary.org/programs/projects/pioneer_anomaly/updates.html
And "begathon"...I like it...captures the tone of those four-page letters nicely...
--Emily
Dear Emily,
Speaking of TPS-funded projects, what has happened with Project BETA? Was the Harvard dish ever repaired? If not, is there an alternate plan to keep BETA running? Or is everything focused on Optical SETI now? And what has happened with that project lately?
Thank you.
Posted by: The Messenger Nov 10 2005, 04:44 PM
QUOTE (lyford @ Nov 9 2005, 11:41 PM)
Call me old fashioned, but I am a bit wary of jettisoning the "old physics" when the effects are at what I understand to be the threshold of detection, and we really don't know what the environment the little guys are swimming in right now is like - we may need to look for a new theory of interstellar wind before altering the laws of motion.
Still it is fun to think about - and it IS possible I suppose -
Pioneer 10 & 11 are not the only odd-ball observations, and I am not talking about rocks that look like a pock-marked Elvis.
Pioneer 6 charted heavy Doppler residuals, and a linear component (similar to the term used in this paper) had to be added to the solar wind to plot both Galileo and Ulysses during interplanetary transitions. There is a possibility that when all the dots are connected, something fundamental will jump out of the wood work.
Posted by: elakdawalla Nov 10 2005, 04:46 PM
QUOTE (ljk4-1 @ Nov 10 2005, 07:33 AM)
Dear Emily, Speaking of TPS-funded projects, what has happened with Project BETA? Was the Harvard dish ever repaired? If not, is there an alternate plan to keep BETA running? Or is everything focused on Optical SETI now? And what has happened with that project lately? Thank you.
That's a good question, and I don't know the answer, and the SETI areas of our website have suffered a bit through the redesign process. We should have answers for you there and we don't. I'll try to follow up. Amir Alexander here at the Society is the one who does SETI, I'll see if he can answer your question.
--Emily
Posted by: lyford Nov 10 2005, 10:06 PM
QUOTE (The Messenger @ Nov 10 2005, 08:44 AM)
Pioneer 10 & 11 are not the only odd-ball observations.... (edit) ....There is a possibility that when all the dots are connected, something fundamental will jump out of the wood work.
True, but we have too few dots right now, and this is another great reason to have more outer solar system missions!
Though, infuriatingly, we will have to wait quite a long time for a return on investment, even for the New Horizons data.
I don't mean to imply that only odd balls that make odd ball observations, and I realize an anomaly to be explained can be a doorway to new understanding - Black Body Radiation anyone?
I find it fascinating nonetheless that the universe is understandable at all, and if you think about it, Science has only had a few centuries to explore the entire span of space time from our little home here. I am sure there are plenty of surprises in store.
Posted by: ljk4-1 Dec 20 2005, 04:05 PM
Astrophysics, abstract
astro-ph/0505310
From: Michael A. Ivanov [view email]
Date (v1): Sat, 14 May 2005 19:34:27 GMT (122kb)
Date (revised v2): Mon, 19 Dec 2005 16:23:51 GMT (124kb)
Low-energy quantum gravity leads to another picture of the universe
Authors: Michael A. Ivanov
Comments: 13 pages, 4 figures, LaTeX. Contribution to the 1st Crisis in
Cosmology Conference (CCC-1), Moncao, Portugal, 23-25 June 2005. A computational error amd some misprints are corrected in this version
If gravitons are super-strong interacting particles and the low-temperature graviton background exists, the basic cosmological conjecture about the Dopplerian nature of redshifts may be false: a full magnitude of cosmological redshift would be caused by interactions of photons with gravitons. Non-forehead collisions with gravitons will lead to a very specific additional relaxation of any photonic flux that gives a possibility of another interpretation of supernovae 1a data - without any kinematics. These facts may implicate a necessity to change the standard cosmological paradigm. Some features of a new paradigm are discussed. In a frame of this model, every observer has two different cosmological horizons. One of them is defined by maximum existing temperatures of remote sources - by big enough distances, all of them will be masked with the CMB radiation. Another, and much smaller, one depends on their maximum luminosity - the luminosity distance increases with a redshift much quickly than the geometrical one.
If the considered quantum mechanism of classical gravity is realized in the nature, then an existence of black holes contradicts to the equivalence principle. In this approach, the two fundamental constants - Hubble's and Newton's ones - should be connected between themselves. The theoretical value of the Hubble constant is computed. Also, every massive body would be decelerated due to collisions with gravitons that may be connected with the Pioneer 10 anomaly.
http://arXiv.org/abs/astro-ph/0505310
Posted by: ljk4-1 Jan 3 2006, 02:31 AM
General Relativity and Quantum Cosmology, abstract
gr-qc/0512121
From: Slava G. Turyshev [view email]
Date: Wed, 21 Dec 2005 21:49:36 GMT (882kb)
The Study of the Pioneer Anomaly: New Data and Objectives for New Investigation
Authors: Slava G. Turyshev, Viktor T. Toth, Larry R. Kellogg, Eunice. L. Lau, Kyong J. Lee
Comments: 42 pages, 40 figures, 3 tables
Radiometric tracking data from Pioneer 10 and 11 spacecraft has consistently indicated the presence of a small, anomalous, Doppler frequency drift, uniformly changing with a rate of ~6 x 10^{-9} Hz/s; the drift can be interpreted as a constant sunward acceleration of each particular spacecraft of a_P = (8.74 \pm 1.33) x 10^{-10} m/s^2. This signal is known as the Pioneer anomaly; the nature of this anomaly remains unexplained. We discuss the efforts to retrieve the entire data sets of the Pioneer 10/11 radiometric Doppler data. We also report on the recently recovered telemetry files that may be used to reconstruct the engineering history of both spacecraft using original project documentation and newly developed software tools. We discuss possible ways to further investigate the discovered effect using these telemetry files in conjunction with the analysis of the much extended Doppler data. We present the main objectives of new upcoming study of the Pioneer anomaly, namely i) analysis of the early data that could yield the direction of the anomaly, ii) analysis of planetary encounters, that should tell more about the onset of the anomaly, iii) analysis of the entire dataset, to better determine the anomaly's temporal behavior, iv) comparative analysis of individual anomalous accelerations for the two Pioneers, v) the detailed study of on-board systematics, and vi) development of a thermal-electric-dynamical model using on-board telemetry. The outlined strategy may allow for a higher accuracy solution for a_P and, possibly, will lead to an unambiguous determination of the origin of the Pioneer anomaly.
http://arxiv.org/abs/gr-qc/0512121
Posted by: tfisher Jan 3 2006, 07:10 AM
I just read through the last paper linked. They've done quite well at recovering a complete data set, including telemetry data like temperature and voltage readouts useful for reconstructing thermal contributions to the Pioneers' accelerations. Another cool tidbit: there is one last opportunity to attempt to contact Pioneer 10, coming up in this February/March. (They think that, just barely maybe there is enough power still now in the old RTGs...) The round-trip light-time is 25 hours, so the contact would proceed by sending out a signal from Goldstone, waiting a day while the earth spins around once and the radio waves make their merry way, and listening for a response again at Goldstone. Somehow that image amuses me :^)
Posted by: ljk4-1 Jan 4 2006, 06:18 PM
Paper: astro-ph/0504367
Date (v1): Sun, 17 Apr 2005 17:04:48 GMT (32kb)
Date (revised v2): Sat, 1 Oct 2005 13:46:27 GMT (43kb)
Date (revised v3): Mon, 2 Jan 2006 16:12:03 GMT (36kb)
replaced with revised version Mon, 2 Jan 2006 16:12:03 GMT (36kb)
Title: Can Minor Planets be Used to Assess Gravity in the Outer Solar System?
Authors: Gary L. Page, David S. Dixon, John F. Wallin
Comments: Accepted for publication in The Astrophysical Journal
The twin Pioneer spacecraft have been tracked for over thirty years as they headed out of the solar system. After passing 20 AU from the Sun, both exhibited a systematic error in their trajectories that can be interpreted as a constant acceleration towards the Sun. This Pioneer Effect is most likely explained by spacecraft systematics, but there have been no convincing arguments that that is the case.
The alternative is that the Pioneer Effect represents a real phenomenon and perhaps new physics. What is lacking is a means of measuring the effect, its variation, its potential anisotropies, and its region of influence.
We show that minor planets provide an observational vehicle for investigating the gravitational field in the outer solar system, and that a sustained observation campaign against properly chosen minor planets could confirm or refute the existence of the Pioneer Effect.
Additionally, even if the Pioneer Effect does not represent a new physical phenomenon, minor planets can be used to probe the gravitational field in the outer Solar System and since there are very few intermediate range tests of gravity at the multiple AU distance scale, this is a worthwhile endeavor in its own right.
\\ ( http://arXiv.org/abs/astro-ph/0504367 , 36kb)
Posted by: tasp Jan 5 2006, 04:14 AM
I bet it is not as simple as this, but I will post an idea and watch it be shredded . . .
Any possibility either Voyager craft could be spun at a few revs per hour, with the thrusters turned off, and keep the dish pointed at earth for maybe a year or two?
My thought is if we could get a confirmation of the Pioneer anomaly with a Voyager craft it might help JPL design a more capable or sophisticated 'Pioneer Anomally Probe' someday.
With the 'nodding' motion compensation used at Triton, I am cautiously optimistic that there might still be a new trick for our favorite 'old dog' to learn.
Having a spin stabilised period of flight for a Voyager might yield enough high quality tracking data at what would have to be an attractive price compared to launching another probe designed for the task.
Besides, I'm getting old and would like this mystery cleared up while I am still around . . .
Posted by: mchan Jan 5 2006, 06:06 AM
QUOTE (tasp @ Jan 4 2006, 08:14 PM)
Any possibility either Voyager craft could be spun at a few revs per hour, with the thrusters turned off, and keep the dish pointed at earth for maybe a year or two?
One problem is that something that was not designed to be spin stabilized (like Voyager) would very likely not spin very well. E.g. the spin axis would move around. In the case of Voyager, a stable spin axis (is such exists) may not align with the axis if the high gain antenna.
Posted by: ugordan Jan 5 2006, 08:52 AM
QUOTE (mchan @ Jan 5 2006, 07:06 AM)
One problem is that something that was not designed to be spin stabilized (like Voyager) would very likely not spin very well. E.g. the spin axis would move around. In the case of Voyager, a stable spin axis (is such exists) may not align with the axis if the high gain antenna.
Wasn't the spacecraft-solid rocket stack spin stabilized for the duration of the rocket's burn during Jupiter injection or was it also in 3-axis stabilization mode? I would have figured delivery errors would be minimized by spinning up first.
Another possible problem with spin-stabilizing is the star sensor, would it be able to cope with starfield smearing during rotation?
Posted by: Bob Shaw Jan 5 2006, 01:16 PM
QUOTE (ugordan @ Jan 5 2006, 09:52 AM)
Wasn't the spacecraft-solid rocket stack spin stabilized for the duration of the rocket's burn during Jupiter injection or was it also in 3-axis stabilization mode? I would have figured delivery errors would be minimized by spinning up first.
Another possible problem with spin-stabilizing is the star sensor, would it be able to cope with starfield smearing during rotation?
If all that's required is a beacon, then setting up a slow spin where the aim point of the antenna nutates around the position of the Earth might be better than a precisely-aimed but data-free arangement. The CG and dynamic behaviour of the Voyagers must be *very* well known by now (unless something has dropped off with the cold). If data is required, that's perhaps another story. Perhaps the lesson here is that future interstellar-precursor probes should be designed with graceful aging in mind, so that as their output of data reduces it still remains - just - there.
Oh, and isn't it good to hear that there's going to be another attempt to reach Pioneer!
Bob Shaw
Posted by: ljk4-1 Jan 5 2006, 02:22 PM
Can New Horizons participate in this experiment? Or was that another item left off the menu?
Posted by: djellison Jan 5 2006, 02:43 PM
QUOTE (ljk4-1 @ Jan 5 2006, 02:22 PM)
Can New Horizons participate in this experiment? Or was that another item left off the menu?
That's an unfair and unjustified jab at the mission.
From http://www.planetary.org/programs/projects/pioneer_anomaly/update_20050720.html
QUOTE (Plan Soc Website)
The Pioneers are spin-stabilized spacecraft. The Voyagers are three-axis stabilized craft that fire thrusters to maintain their orientation in space or to slew around and point their instruments. Those thruster firings would introduce uncertainties in the tracking data that would overwhelm any effect as small as that occurring with Pioneer.
This difference in the way the spacecraft are stabilized actually is one of the reasons the Pioneer data are so important and unique. Most current spacecraft are three-axis stabilized, not spin stabilized. It is unlikely another spin-stabilized craft will be sent across the solar system in the foreseeable future.
Doug
Posted by: tasp Jan 5 2006, 02:45 PM
If an objection to putting a Voyager into a slow spin is the likelihood that it would not be possible to stop the spin, do we care?
{well, of course we care, but you catch my drift}
IIRC, some of the fields and particle experiments on Voyager work better when the craft is spinning, and the craft has spun for short periods for that very reason during planetary encounters.
Maybe this isn't so unlikely?
Posted by: ugordan Jan 5 2006, 02:50 PM
QUOTE (djellison @ Jan 5 2006, 03:43 PM)
That's an unfair and unjustified jab at the mission.
No - it cant, because it uses thrusters to manouver which would impart a small, but hard to calculate delta-V every time the spacecraft pitches, rolls and yaws. Same reason that Voyager is of no use either.
Yes, but unlike the Voyagers, NH also has a spin mode which will be used during the long interplanetary cruise. So we might get long intervals when the s/c will be spin-stabilized and use it to get periods of precise tracking data. This will of course not be possible during the Jupiter encounter as well as the Pluto encounter phase, but at all other times (assuming thrusters will be off) it should be possible.
Seven years or so between Jupiter flyby and start of Pluto approach phase is a pretty good sample, IMHO.
Posted by: djellison Jan 5 2006, 02:58 PM
Damn good point actually UG - hadnt thought of that.
Then again, they're planning a yearly checkout iirc though - and that may involved pitching/rolling/yawing the spacecraft to look at astronomical calibration targets, which would trash the effect wouldnt it?
QUOTE (pluto.jhuapl.edu)
activities during the approximately 8-year cruise to Pluto include annual spacecraft and instrument checkouts, trajectory corrections, instrument calibrations and Pluto encounter rehearsals.
Doug
Posted by: ugordan Jan 5 2006, 03:05 PM
QUOTE (djellison @ Jan 5 2006, 03:58 PM)
Then again, they're planning a yearly checkout iirc though - and that may involved pitching/rolling/yawing the spacecraft to look at astronomical calibration targets, which would trash the effect wouldnt it?
I don't think it would trash the effect. At least much. They'll still have periods of inertial coast in between and still see if the modelled-out Doppler plots fit with the observed segments. A residual should still be detectable, though it won't take time do reach a big, nice and well-detectable magnitude before another "trashing" period. Then again, the s/c will probably have more stable RF oscillators so the balance could still hold.
On the other side, I vaguely *seem* to remember reading somewhere that NH actually won't be a good tool to measure the acceleration, I forget why.
Might have been something with the ultrastable oscillators thing.
Might have been a pigment of my imagination...
Posted by: NMRguy Jan 5 2006, 05:19 PM
QUOTE (Alan Stern @ Feb 23 2005, 09:20 AM)
Yes, we spin most of cruise, stopping only rarely. It costs fuel that we want to hoard for encounters and KBO DeltaV. And yes, our radio science team hopes to look for
the Pioneer anaomaly. Contact Len Tyler or Ivan Linscott at Stanford.
-Alan
Alan addressed this back in Feb 05 in the "New Horizons, Pluto and the Kuiper belt" page. It seems like he plans to take full advantage of this opportunity.
Posted by: AlexBlackwell Jan 5 2006, 05:56 PM
QUOTE (NMRguy @ Jan 5 2006, 05:19 PM)
Alan addressed this back in Feb 05 in the "New Horizons, Pluto and the Kuiper belt" page. It seems like he plans to take full advantage of this opportunity.
Below is an excerpt from The Planetary Society's website of http://www.planetary.org/programs/projects/pioneer_anomaly/update_200511.html:
QUOTE
[Slava] Turyshev introduced the possibility of working with New Horizons, NASA’s Pluto-Kuiper belt mission scheduled to launch on January 11, 2006. The Pioneer anomaly investigation team was invited to come up with a thermal model of the New Horizons spacecraft. New Horizons was developed very rapidly on a very small budget. New Horizons was developed so quickly in order to catch the small launch period that is available to get a Jupiter fly by on the way to Pluto, which cuts flight time by a few years.
New Horizons is a great mission for us to look at; they have a spin-stabilized craft, the Doppler data will be very good (not as good as Cassini, but better than Pioneer), and it will be going out to Pluto (remember we found the Pioneer anomaly at the distance of Saturn)! As Turyshev put it, this is a once in a lifetime opportunity.
Sounds great, right?! Unfortunately, the funding for New Horizons is already limited and we will have to bring our own funding, as well as figuring out the study itself. So, time will tell if this works out.
Posted by: tty Jan 5 2006, 06:47 PM
QUOTE (ugordan @ Jan 5 2006, 05:05 PM)
Might have been a pigment of my imagination...
Just what colour
is your imagination?
tty
Posted by: Stephen Jan 8 2006, 05:02 PM
QUOTE (Merek Chertkow's report)
http://www.planetary.org/programs/projects/pioneer_anomaly/update_200511.html
"Turyshev and John Anderson, also of JPL, with financial support from The Planetary Society were able to save this additional information from simply being thrown in the dumpster! I know what you must be thinking! I can’t believe it either!"
That sounds just like the anecdote Don Wilhelms tells in "To a Rocky Moon"! When will NASA learn stop throwing its treasures out with the trash?
Posted by: Steffen Jan 9 2006, 07:07 AM
Sorry, but what is this anomaly about?
( I'm a Newbie asking too many questions )
Posted by: elakdawalla Jan 9 2006, 04:26 PM
QUOTE (Steffen @ Jan 8 2006, 11:07 PM)
Sorry, but what is this anomaly about?
( I'm a Newbie asking too many questions )
Google searches will answer lots of questions -- try here for starters.
http://www.planetary.org/programs/projects/pioneer_anomaly/
--Emily
Posted by: Planet X Jan 9 2006, 04:47 PM
QUOTE (tfisher @ Jan 3 2006, 01:10 AM)
Another cool tidbit: there is one last opportunity to attempt to contact Pioneer 10, coming up in this February/March. (They think that, just barely maybe there is enough power still now in the old RTGs...) The round-trip light-time is 25 hours, so the contact would proceed by sending out a signal from Goldstone, waiting a day while the earth spins around once and the radio waves make their merry way, and listening for a response again at Goldstone. Somehow that image amuses me :^)
Cool! I hope they attempt it and it's successful. Later!
J P
Posted by: djellison Jan 9 2006, 04:50 PM
I have an image in my head of driving around the M25 ( the london 'orbital' motorway ) and yelling at a service station "BIG MAC AND FRIES PLEASE"...then doing another lap of the motorway, only to have a burger land on my windscreen about 80 miles later once I was back in the same place
Doug
Posted by: The Messenger Jan 9 2006, 05:24 PM
QUOTE (Steffen @ Jan 9 2006, 12:07 AM)
Sorry, but what is this anomaly about?
( I'm a Newbie asking too many questions )
Here is a concise summary by the three principles:
http://arxiv.org/PS_cache/gr-qc/pdf/0411/0411077.pdf
And if you want to see how exhaustively this phenomena has been explored, here is another 55 pages:
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf
NASA's unwillingness to fund a follow-up mission, or even preserve historical data that may shed additional light is disheartening. We know our physical models are close, and we also know exceptions that may require new models, if they exist, must be hiding in the fringes. Anderson & company have tried every avenue they can imagine to null this anomaly as an artifact, and have been unable to do so.
Posted by: JRehling Jan 9 2006, 09:29 PM
QUOTE (The Messenger @ Jan 9 2006, 09:24 AM)
NASA's unwillingness to fund a follow-up mission, or even preserve historical data that may shed additional light is disheartening.
[...]
Anderson & company have tried every avenue they can imagine to null this anomaly as an artifact, and have been unable to do so.
From a risk assessment basis, I don't find it disheartening that no dedicated mission is on the books. For one, it's possible (even if unlikely, and I mean no disrespect to Anderson et al) that future analysis will lead to a forehead-slapping resolution to the anomaly. That head-slap would be a lot harder if we had a $150 million mission already in interplanetary cruise for no good reason when the anomaly were understood. It's also possible that a future mission could investigate this completely in line with its other, primary goals.
There is no way we can investigate various outer solar system objects in great detail without visits from spacecraft. There's no chance that an ingenious look at old data will suddenly give us maps of the unseen hemispheres of the uranian moons. But in this case, there is a chance, and there's no urgency to resolving the mystery before the ground on which it rests has been plowed into dust by means much, much cheaper than a spacecraft.
The disregard for the existing data is rather more disheartening, but simply goes to show how things can be neglected for their due worth by a boxology-driven bureaucracy like NASA.
Posted by: Richard Trigaux Jan 9 2006, 09:34 PM
QUOTE (JRehling @ Jan 9 2006, 09:29 PM)
From a risk assessment basis, I don't find it disheartening that no dedicated mission is on the books. For one, it's possible (even if unlikely, and I mean no disrespect to Anderson et al) that future analysis will lead to a forehead-slapping resolution to the anomaly. That head-slap would be a lot harder if we had a $150 million mission already in interplanetary cruise for no good reason when the anomaly were understood. It's also possible that a future mission could investigate this completely in line with its other, primary goals.
There is no way we can investigate various outer solar system objects in great detail without visits from spacecraft. There's no chance that an ingenious look at old data will suddenly give us maps of the unseen hemispheres of the uranian moons. But in this case, there is a chance, and there's no urgency to resolving the mystery before the ground on which it rests has been plowed into dust by means much, much cheaper than a spacecraft.
The disregard for the existing data is rather more disheartening, but simply goes to show how things can be neglected for their due worth by a boxology-driven bureaucracy like NASA.
I agree with this, especially with the conclusion. THE EXISTING DATA MUST BE KEPT SAFE and analyzed completelly. The results must be confirmed by other flights (of which it can be a secondary goal) before sending a dedicated mission.
Posted by: Mongo Jan 9 2006, 11:20 PM
If the unmodeled acceleration is indeed, as the evidence suggests, about 0.00000008 cm-per-second per second, then since 1980 (when the effect first definitely appears) there would be a cumulative unmodeled delta-v of about 17 metres-per-second towards the Sun, and a cumulative unmodeled spatial displacement of about 269,000 km toward the Sun.
Given the upcoming opportunity for a com session with one of the Pioneers, this would result in a round-trip time almost two seconds shorter than what it 'should' be. Although it is still about 25 hours.
Bill
Posted by: ljk4-1 Jan 10 2006, 02:34 AM
QUOTE (Mongo @ Jan 9 2006, 06:20 PM)
If the unmodeled acceleration is indeed, as the evidence suggests, about 0.00000008 cm-per-second per second, then since 1980 (when the effect first definitely appears) there would be a cumulative unmodeled delta-v of about 17 metres-per-second towards the Sun, and a cumulative unmodeled spatial displacement of about 269,000 km toward the Sun.
Given the upcoming opportunity for a com session with one of the Pioneers, this would result in a round-trip time almost two seconds shorter than what it 'should' be. Although it is still about 25 hours.
Bill
Is there any way to tell if small planetoids or comets are undergoing the same effect? Or are they just too big and their orbits - especially the ones farther out - just not known well enough?
Heck, while I'm at it - has anyone investigated to see if Dark Matter exists not just outside galaxies but in interstellar space as well? Perhaps closer than we think?
Posted by: Mongo Jan 10 2006, 05:29 AM
QUOTE (ljk4-1 @ Jan 10 2006, 02:34 AM)
Heck, while I'm at it - has anyone investigated to see if Dark Matter exists not just outside galaxies but in interstellar space as well? Perhaps closer than we think?
I personally am less than convinced of the existence of so-called Dark Matter.
The problem for me is that:
1) New physics is needed to account for its existence.
2) In order for it to account for the observed galactic rotation curves (which is why it was originally proposed), the distribution of 'Dark Matter' in each galaxy must be carefully adjusted by radius from the galactic center in order to match the needed gravitational potentials. This distribution needs to vary wildly from one galaxy to the next, in order to produce rotation curves that are far more similar to each other than they 'should be'.
3) No candidate Dark Matter particles have ever been detected.
Compare this with Mordehai Milgrom's MOND theory, which was also designed to explain galactic rotation curves:
1) New physics is needed to account for the deviations from Newtonian physics. Okay, so far the two explanations are a wash.
2) MOND naturally explains galactic rotation curves with little or no special adjustment, by assuming that the visible matter (including gas and dust) is in fact all there is. The theory was used to make predictions of rotation curves for classes of galaxies (i.e. low surface-brightness galaxies) that were unknown when it was introduced, that have panned out exactly. Dark Matter, on the other hand, made wildly inaccurate predictions, that must be corrected ex post facto.
3) The same physics that seems to be behind MOND can also explain so-called 'Dark Energy' and, in certain formulations, even the Pioneer Effect,
Here are some papers about MOND:
The arXiv papers of the originator, Mordehai Milgrom, regarding MOND:
http://xxx.lanl.gov/find/astro-ph/1/AND+au:+milgrom+abs:+MOND/0/1/0/all/0/1
TeVeS, the currently most popular relativistic formulation of MOND:
http://xxx.lanl.gov/find/astro-ph/1/abs:+TeVeS/0/1/0/all/0/1
Bill
Posted by: ljk4-1 Jan 10 2006, 01:55 PM
This site gives the general history and background on MOND, including links to other sites:
http://en.wikipedia.org/wiki/MOND
Posted by: ljk4-1 Jan 10 2006, 04:29 PM
Astrophysics, abstract
astro-ph/0503368
From: Dario N\'u\~nez [view email]
Date (v1): Wed, 16 Mar 2005 19:54:33 GMT (409kb)
Date (revised v2): Mon, 9 Jan 2006 17:37:29 GMT (421kb)
Pioneer anomaly? Gravitational pull due to the Kuiper belt
Authors: Jose A. de Diego, Dario Nunez, Jesus Zavala
Comments: 5 figures, final version, accepted for publication at Int. J. of Mod. Phys. D
In this work we study the gravitational influence of the material extending from Uranus orbit to the Kuiper belt and beyond on objects moving within these regions. We conclude that a density distribution given by $\rho®=\frac{1}{r}$ (for $r\geq 20 UA$) generates a constant acceleration towards the Sun on those objects, which, with the proper amount of mass, accounts for the blue shift detected on the Pioneers space crafts. We also discuss the effect of this gravitational pull on Neptune, and comment on the possible origin of such a matter distribution.
http://arxiv.org/abs/astro-ph/0503368
Posted by: The Messenger Jan 10 2006, 06:54 PM
QUOTE (ljk4-1 @ Jan 10 2006, 09:29 AM)
Astrophysics, abstract
astro-ph/0503368
From: Dario N\'u\~nez [view email]
Date (v1): Wed, 16 Mar 2005 19:54:33 GMT (409kb)
Date (revised v2): Mon, 9 Jan 2006 17:37:29 GMT (421kb)
Pioneer anomaly? Gravitational pull due to the Kuiper belt
Authors: Jose A. de Diego, Dario Nunez, Jesus Zavala
Comments: 5 figures, final version, accepted for publication at Int. J. of Mod. Phys. D
In this work we study the gravitational influence of the material extending from Uranus orbit to the Kuiper belt and beyond on objects moving within these regions. We conclude that a density distribution given by $\rho®=\frac{1}{r}$ (for $r\geq 20 UA$) generates a constant acceleration towards the Sun on those objects, which, with the proper amount of mass, accounts for the blue shift detected on the Pioneers space crafts. We also discuss the effect of this gravitational pull on Neptune, and comment on the possible origin of such a matter distribution.
http://arxiv.org/abs/astro-ph/0503368
Anderson & Co. wrote a response to this - Essentially this type of mass could NOT produce the measured linearity - the probe should be accelerating at an increasing rate (if the Kuiper belt has a high enough density), and/or the density would have to extend to near the orbit of Saturn and therefore be easily be detectable.
MOND is not theoretically based - it is purely a phenomological explanation of a rather confusing family of observations.
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf
QUOTE
Page 22:
The Aerospace’s analysis of the Galileo data covered the same arc as JPL and a second arc from 2 December 1992 to 24 March 1993. The analysis of Doppler data
from the first arc resulted in a determination for aP of ∼ (8 ± 3) × 10−8 cm/s2, a value similar to that from Pioneer 10. But the correlation with solar pressure was
so high (0.99) that it is impossible to decide whether solar pressure is a contributing factor...
...So, by interpreting this time variation as a true r−2 solar
pressure plus a constant radial acceleration, we found that Ulysses was subjected to an unmodeled acceleration towards the Sun of (12 ± 3) ×10−8 cm/s2.
Note, however, that the determined constant aP(U) is highly correlated with solar radiation pressure (0.888).
This shows that the constant acceleration and the solar radiation acceleration are not independently determined, even over a heliocentric distance variation from 5.4 to 1.3 AU.
Four independent data point should lead to a little bit more than head scratching. True, an independent mission is prohibitively expensive, but piggy-backing a frizbee on the New Horizon's probe: spin stabilized, with a Doppler repeater similar to the Pioneer probes - that could have been a reasonably cheap and lightweight add-on with enough parametric control to nail this puppy down.
Posted by: Jeff7 Jan 10 2006, 11:30 PM
Concerning dark matter, I remembered some article that had a theory for why dark matter need not exist at all - that we only need to use relativity properly, and apply it to gravity. Something along those lines.
http://www.cerncourier.com/main/article/45/8/8 - it has a summary of this theory, and a link to the full abstract. It seems to say that, when looking at something small, like a single star, Newtonian physics may be an adequate approximation, but this doesn't work when you're looking at the way an entire galaxy behaves.
Posted by: ljk4-1 Jan 11 2006, 04:31 PM
Anomalous Acceleration of Pioneer 10 and 11: Dust Density in the Kuiper Belt
http://www.newtonphysics.on.ca/Anomalous/Acceleration.html
And this BBC item from 1999 may be of interest:
http://news.bbc.co.uk/1/hi/sci/tech/460095.stm
Relevant information on the Kuiper Belt:
http://www.lpl.arizona.edu/faculty/malhotra_preprints/ISP_Nov04.html
http://www.lpl.arizona.edu/faculty/malhotra_preprints/04-TPF_Darwin.pdf
Posted by: Myran Jan 11 2006, 07:37 PM
Thank you ljk4-1, that first link was interesting indeed.
So it might simply be dust?
Well its the simplest explanation, so im inclined more to that one than some of the other proposals.
As for the final destiny of the spacecrafts, that they would aquire so much dust eventually was a surprise to me:
"Pioneer spacecraft will become the nucleus of asteroids flying away from the solar system with the interstellar dust. "
Posted by: Mongo Jan 11 2006, 08:28 PM
QUOTE (Jeff7 @ Jan 10 2006, 11:30 PM)
Concerning dark matter, I remembered some article that had a theory for why dark matter need not exist at all - that we only need to use relativity properly, and apply it to gravity. Something along those lines.
http://www.cerncourier.com/main/article/45/8/8 - it has a summary of this theory, and a link to the full abstract. It seems to say that, when looking at something small, like a single star, Newtonian physics may be an adequate approximation, but this doesn't work when you're looking at the way an entire galaxy behaves.
Here are the direct links for the original paper:
http://xxx.lanl.gov/abs/astro-ph/0507619
and for its follow-ip:
http://xxx.lanl.gov/abs/astro-ph/0512048
These two paper are interesting indeed! Their argument is that galactic rotation curves have always been modeled using Newtonian Gravity (NG) rather than the full General Relativity (GR), because GR is so much harder to model for something like a galaxy. In fact, even today it is impossible to accurately model a galaxy with GR, the two papers describe highly simplified models. Everyone assumed that there would be little difference between the results using NG and GR, but the authors show that there is actually a huge difference in the results.
Models using NG predict, from the visible matter, rotation curves that fall far short of observations, requiring new physics as a result: either invisible 'Dark Matter', that does not fit into the Standard Theory of physics derived from direct experiment, or a theory of MOND that modifies either gravity or inertia. The (highly simplified) model using GR, on the other hand, predicts rotation curves that closely match observations, obviating the need for 'Dark Matter' or MOND.
I should point out, however, that MOND was always a phenomenological theory, and its predictions using visible matter would closely match the predictions using GR. In other words, MOND was describing the effects of GR on galaxies, without realising it!
Will these papers have the influence on cosmology that they seem to deserve? The problem is that almost all of modern cosmology is based on the assumption that 'Dark Matter' exists. Most current cosmologists have based their careers on this assumption. They would be VERY reluctant to throw so much of their professional work away.
I would like to see follow-ups to these papers, but right now I am inclined to think that galactic rotation curves are indeed accurately described by GR, without the need for 'Dark Matter'.
Bill
Posted by: Richard Trigaux Jan 11 2006, 09:03 PM
QUOTE (Mongo @ Jan 11 2006, 08:28 PM)
Will these papers have the influence on cosmology that they seem to deserve? The problem is that almost all of modern cosmology is based on the assumption that 'Dark Matter' exists. Most current cosmologists have based their careers on this assumption. They would be VERY reluctant to throw so much of their professional work away.
Bill
However an explanation of galactic behaviour without extra hypothesis would be fine.
A note is that dark matter is suggested, not only by the rotation curve, but also by gravitationnal lens effects, which suggest a mass 10 to 100 times more that of visible stars.
An idea of mine was to derive the state equation of the "dark matter" from the rotation curve. (the rotation curve gives the mass as a function of the distance to center, which gives density. From all the mass "above", we get the pressure). Easy at a first glance, but there is a differential equation to solve, a bit beyond my possibilities. And the result may be very different if we consider the matter is in a disk or in a sphere. Also the equation can be properly solved only if we have an upper limit to the mass repartition. So I was not sure of the result.
Recently, the observation of gravitationnal lens effects allowed to build density profiles in far galaxies and clusters. So the differential equation can be solved numerically, and I had hints it was done. But I never see any result. However this would give serious clues about what is dark matter. For instance finding that the state equation has a power law of 1.4 would make quasi-certain that the dark matter is neutral molecular hydrogen. Other candidates, dust, stars or subatomic particules would give other signatures.
Posted by: ljk4-1 Jan 11 2006, 09:42 PM
Judging by these two new news items, dark matter/energy cosmology is indeed the "in" topic for astronomers these days.
Johns Hopkins Univ. news release dated 1/11/06
SCIENTISTS "RAVE-ING" ABOUT MOST AMBITIOUS STAR SURVEY EVER
An international team of astronomers today announced the first results from
the Radial Velocity Experiment, an ambitious all-sky spectroscopic survey
aimed at measuring the speed, temperature, surface gravity and composition
of up to a million stars passing near the sun.
Those first results from the project, known for short as RAVE, confirm that
dark matter dominates the total mass of our home galaxy, the Milky Way, team
members at The Johns Hopkins University and elsewhere said. The full survey
promises to yield a new, detailed understanding of the origins of the
galaxy, they said.
The results were released at the American Astronomical Society's 207th
meeting in Washington, D.C.
An image is available at http://www.jhu.edu/news/home06/jan06/wyse.html
Gamma-ray burst study may rule out cosmological constant
Dark energy - the mysterious force that drives the acceleration of
the universe - changes over time, suggest controversial new
calculations.
If true, the work rules out Einstein's notion of a "cosmological
constant" and suggests dark energy, which now repels space, once
drew it together.
Read the full story on New Scientist Space:
http://www.newscientistspace.com/article/dn8566
Posted by: Mongo Jan 11 2006, 09:48 PM
QUOTE (Richard Trigaux @ Jan 11 2006, 09:03 PM)
A note is that dark matter is suggested, not only by the rotation curve, but also by gravitationnal lens effects, which suggest a mass 10 to 100 times more that of visible stars.
Another effect is the apparent 'extra mass' in galaxy clusters suggested by the observed excess galactic velocities.
However, the authors point out that the virial theorem, which is the basis of this supposed extra mass, is itself based on Newtonian Gravity. As far as I know, nobody has tried to model galaxy clusters using General Relativity. Given the huge apparent difference that GR versus NG makes in modeling galactic rotation curves, it would not surprise me at all if GR eliminated the 'extra mass' (beyond the already-known hot gas, etc.) in galaxy clusters.
As for the magnitude of the gravitational lens effect, I am not in a position to comment. Were those mass calculations done using full GR modeling of a rotating galaxy, or they done by treating the galaxies as a 'point source' of gravitational distortion? It sounds like galaxies as a whole have a larger second-order gravitational effect under GR than had been expected.
Bill
Posted by: Mongo Jan 11 2006, 10:00 PM
QUOTE (ljk4-1 @ Jan 11 2006, 09:42 PM)
Those first results from the project, known for short as RAVE, confirm that
dark matter dominates the total mass of our home galaxy, the Milky Way, team
members at The Johns Hopkins University and elsewhere said. The full survey
promises to yield a new, detailed understanding of the origins of the
galaxy, they said.
http://www.newscientistspace.com/article/dn8566
Of course it proves nothing of the sort. This is a perfect example of circular reasoning: they assume that dark matter exists and analyse the results given that assumption. All that this survey shows is that the local stars have orbital velocities higher than that predicted using Newtonian Gravity -- which has been known for decades. It is true that this survey covers more stars, with more accuracy than earlier surveys, but nothing really new has been discovered.
Unless it is disproven, I will go with the idea that the excess orbital velocities are an illusion, due to using Newtonian Gravity rather than General Relativity in the models.
Bill
Posted by: Jeff7 Jan 12 2006, 12:21 AM
QUOTE
I should point out, however, that MOND was always a phenomenological theory, and its predictions using visible matter would closely match the predictions using GR. In other words, MOND was describing the effects of GR on galaxies, without realising it!
Something else, with modeling something like a galaxy, and failing to take general relativity into account - with a few billion individual stars to model, and if Newtonian physics introduces a tiny amount of error with each star in the model, those small deviations will really compound each other. Each star interacts with others, and if those interactions themselves are in error because of initial errors, etc etc etc - billions of tiny errors add up to one big problem.
It sort of surprised me when I read about this, like "well yeah, duh, general relativity. Why aren't you using it already?" I just think it makes sense, now that we have a theory of relativity, that we actually
use it, rather than invent a kind of matter that we just can't directly observe in any fashion.
http://www.jeff7.com/images/anti%20drug%20-%20newtonian%20physics.jpg
(I can't take credit, I just found it online somewhere awhile ago.)
But really, we can't disprove dark matter. Star Trek Voyager proved that it existed when they encountered a dark matter asteroid.
Posted by: The Messenger Jan 12 2006, 03:56 AM
QUOTE (Jeff7 @ Jan 11 2006, 05:21 PM)
It sort of surprised me when I read about this, like "well yeah, duh, general relativity. Why aren't you using it already?" I just think it makes sense, now that we have a theory of relativity, that we actually
use it, rather than invent a kind of matter that we just can't directly observe in any fashion.
http://www.jeff7.com/images/anti%20drug%20-%20newtonian%20physics.jpg
(I can't take credit, I just found it online somewhere awhile ago.)
Three problems with using GR to account for missing galactic mass:
1) GR theoriest did not predict the missing mass - tweaking GR parameters so that they effectively model overaggressive rotational velocities is just curve fitting.
2) Dark matter and energy are needed to literally fill the gaps in the Cosmic Microwave Background. Without dark matter, the CMB power function falls why short of BB model expectations.
3) No gravity waves. Unless and until GWs are detected, all the curve fitting in the world cannot solidify relativistic theory. To date, it can reasonably be argued that we have lacked the needed sensitivity, but this is no longer true. The constraints are such that if LIGO does not detect anything in the next half decade, we are looking down the barrel of another Michelson Morley null.
Posted by: Mongo Jan 12 2006, 05:13 AM
QUOTE (The Messenger @ Jan 12 2006, 03:56 AM)
Three problems with using GR to account for missing galactic mass:
1) GR theoriest did not predict the missing mass - tweaking GR parameters so that they effectively model overaggressive rotational velocities is just curve fitting.
2) Dark matter and energy are needed to literally fill the gaps in the Cosmic Microwave Background. Without dark matter, the CMB power function falls why short of BB model expectations.
3) No gravity waves. Unless and until GWs are detected, all the curve fitting in the world cannot solidify relativistic theory. To date, it can reasonably be argued that we have lacked the needed sensitivity, but this is no longer true. The constraints are such that if LIGO does not detect anything in the next half decade, we are looking down the barrel of another Michelson Morley null.
1) Since it appears that nobody had ever actually created a GR model of galaxy rotation before last year -- due to the computational difficulty of using full GR -- it is no surprise that no predictions were made. On the other hand, once a GR model was made, it produced results close to observations. No 'tweaking' was required.
2) There are four (2x2) possibilities: GR is accurate or not, and BB models use full GR or not.
If the BB models don't assume full GR, then they are flawed from the beginning, given the results described in the rotation curve papers. If the BB models assume full GR, but GR is inaccurate, then the BB models are worthless. On the other hand, if GR is accurate, then it predicts galactic rotation curves that match observations closely enough that there is no place for dark matter anywhere near a galaxy. Given a choice between GR and dark matter, I will choose GR every time. The CMB power function may well be explained by 'new physics' -- possibly related to the Pioneer Anomoly -- but it does not have to be the currently popular CDM + Lambda.
3) Once gravity waves are conclusively disproven, then we can talk. Until then, I will continue to accept that GR is a closer fit to 'reality' than Newtonian Gravity. In any case, even if GR is disproven, its replacement could very well show similar effects on a galactic scale.
Bill
Posted by: Richard Trigaux Jan 12 2006, 09:35 AM
The density of galaxies was determined using the local lens effect, so that it allows to draw a density map of the galaxy. It is as if the galaxy was a glass lens: observing the distortion of the background through it allows to derive a map of the glass lens thickness.
And this allows us to have numeric data on the density of galaxies, not a formula in the style 1/R2 or 1/R3. This in turns allows to solve the differential equation numerically, not algebrically (using numbers and computer calculus, not formulas).
QUOTE (ljk4-1 @ Jan 11 2006, 09:42 PM)
Johns Hopkins Univ. news release dated 1/11/06
SCIENTISTS "RAVE-ING" ABOUT MOST AMBITIOUS STAR SURVEY EVER
An international team of astronomers today announced the first results from
the Radial Velocity Experiment, an ambitious all-sky spectroscopic survey
aimed at measuring the speed, temperature, surface gravity and composition
of up to a million stars passing near the sun.
Those first results from the project, known for short as RAVE, confirm that
dark matter dominates the total mass of our home galaxy, the Milky Way, team
members at The Johns Hopkins University and elsewhere said. The full survey
promises to yield a new, detailed understanding of the origins of the
galaxy, they said.
The results were released at the American Astronomical Society's 207th
meeting in Washington, D.C.
An image is available at http://www.jhu.edu/news/home06/jan06/wyse.html
Very interesting indeed, but they assume that all the stars in the galaxy have elliptic orbits. This is simply not true, and may account with many difficulties.
If a majority of the mass is concentrated into the galaxy plane, stars into inclinated orbits will have chaotic trajectories.
Even stars in the disk plane will not have elliptic orbits, if the mass is into the disk.
The only stars with regular orbits are those in a circular orbit around the center of the galaxy.
Why? because they "feel" the mass "under" them (closer to the centre) as a point mass, and the mass "above" (further from the centre) has no influence. (and even this is not sure, it is true only if the galaxy has a spherical symmetry.)
So until now I even don't know if a spiral galaxy like ours has a spherical symmetry or a disk symmetry. Maybe all the galaxies are more or less elliptic.
However only a precise density map of the supposed dark matter can lead to its state equation, and from there to its physical nature: molecular hydrogen, atomic hydrogen, baryonic objects (ranging from dust to small stars and black holes) or other subatomic particules. If the state equation points at none of these things, so we will have to admitt that there is no dark matter, but some geometric effect.
Posted by: ljk4-1 Jan 12 2006, 10:28 PM
Paper: astro-ph/0601247
Date: Wed, 11 Jan 2006 20:05:34 GMT (7kb)
Title: Alternative proposal to modified Newton dynamics (MOND)
Authors: Juan M. Romero and Adolfo Zamora
Comments: 4 pages. Accepted for publication in PRD
\\
From a study of conserved quantities of the so-called Modified Newtonian
Dynamics (MOND) we propose an alternative to this theory. We show that this
proposal is consistent with the Tully-Fisher law, has conserved quantities
whose Newtonian limit are the energy and angular momentum, and can be useful to explain cosmic acceleration. The dynamics obtained suggests that, when
acceleration is very small, time depends on acceleration. This result is
analogous to that of special relativity where time depends on velocity.
\\ ( http://arXiv.org/abs/astro-ph/0601247 , 7kb)
Posted by: ljk4-1 Jan 13 2006, 02:44 PM
I don't want this turning into the Dark Matter/Energy Topic (unless of course that is what is affecting the Pioneer probes), but I wanted to share this news item while we are still on the subject:
Dark Matter Galaxy?
Summary - (Thu, 12 Jan 2006) Astronomers think they might have found a "dark galaxy", that has no stars and emits no light. Although the galaxy itself, located 50 million light years from Earth, is practically invisible, it contains a small amount of neutral hydrogen which emits radio waves. If astronomers are correct, this galaxy contains ten billion times the mass of Sun, but only 1% of this is hydrogen - the rest is dark matter.
http://www.universetoday.com/am/publish/pparc_darkmatter_virgohi.html?1212006
If there is life in that galaxy, just try to imagine how utterly different it probably is from ours.
Posted by: Richard Trigaux Jan 13 2006, 03:33 PM
QUOTE (ljk4-1 @ Jan 13 2006, 02:44 PM)
I don't want this turning into the Dark Matter/Energy Topic (unless of course that is what is affecting the Pioneer probes), but I wanted to share this news item while we are still on the subject:
Dark Matter Galaxy?
Summary - (Thu, 12 Jan 2006) Astronomers think they might have found a "dark galaxy", that has no stars and emits no light. Although the galaxy itself, located 50 million light years from Earth, is practically invisible, it contains a small amount of neutral hydrogen which emits radio waves. If astronomers are correct, this galaxy contains ten billion times the mass of Sun, but only 1% of this is hydrogen - the rest is dark matter.
http://www.universetoday.com/am/publish/pparc_darkmatter_virgohi.html?1212006
If this is confirmed, it rules out any alternative explanation about dark matter, such as geometric effects, MOND theory, etc and left us only to accept the fact that there is an unknown mass.
QUOTE (ljk4-1 @ Jan 13 2006, 02:44 PM)
If there is life in that galaxy, just try to imagine how utterly different it probably is from ours.
We have no idea until now about what is dark matter. This observation also weakens any explanation based on dwarf stars, black holes, dust, etc... as these objects would be visible in a way or another, at least colectively.
The better explanation left is about weakly interactive particulres (neutrinos or other) which are not a good life support (they don't interact with each other).
But we really don't know, and there is perhaps some kind of alternate universe, with its own stars, or very novel structures, supportive for life.
But I don't believe too much to "dark stars", as if so there would be black holes formed by dark matter, and then ordinary matter spiraling around them, which would be visible.
Posted by: Mongo Jan 13 2006, 05:14 PM
So this team has observed a cloud of neutral hydrogen with an estimated mass of 100 million suns, which has a much too large rotational velocity for its mass. This is the logical end point of the trend from high-surface-brightness elliptical galaxies, which have only slightly too large rotational velocitys, through normal spiral galazies, which have larger excess rotational velocitys, through low-surface-brightness galaxies, which have extreme excess rotational velocities, and finally this lowest-surface-brightness galaxy (which is what this object really is), which has the highest excess rotational velocity of all.
Looks like a trend to me.
I fail to see that this proves that dark matter exists, since the same MOND-like physics (which apparently describe full General Relativity) that were postulated to explain other cases would presumably apply to this object as well. The whole point of MOND-like theories is that they apply under conditions of galactic distances but low gravitational acceleration, which is why the difference between Newtonian models and observation increases with declining surface brightness (which tracks mass and hence gravitational acceleration). Something like this gas cloud would be expected to have remarkably high rotational velocitys.
I think that we should wait to see from a refereed paper if this object is explainable under MOND or GR before proclaiming that dark matter exists.
Bill
Posted by: The Messenger Jan 15 2006, 07:39 AM
QUOTE (Mongo @ Jan 13 2006, 10:14 AM)
I think that we should wait to see from a refereed paper if this object is explainable under MOND or GR before proclaiming that dark matter exists.
Bill
I think we better wait longer that that - there are many refereed papers that all-but-insist Dark Matter is a done deal. Sorry - I don't believe in the Easter Bunny, and I don't believe theories that cannot be demonstrated using local observables and principles are scientifically valid.
There has been an intense campaign in the last four decades to identify the baryons responsible for altering galactic rotations, and these careful seaches have turned up naughta. Most of the conjecture I have seen about why these searches have failed; and how Dark Matter can best be explained have involved hypotheses that simply cannot be tested - and yes, this includes redistributing galactic masses so that General Relativity fits the bill.
The Pioneer anomalies are observational events that we can sink our teeth into. This is where the trail should be picked up - in our own backyard. This is where we can either support or null a hypothesis.
Posted by: ljk4-1 Jan 18 2006, 03:30 PM
Paper (*cross-listing*): gr-qc/0601055
Date: Sat, 14 Jan 2006 16:11:23 GMT (36kb)
Title: What do the orbital motions of the outer planets of the Solar System
tell us about the Pioneer Anomaly?
Authors: Lorenzo Iorio
Comments: Latex2e, 12 pages, 3 tables, 4 figures
Subj-class: General Relativity and Quantum Cosmology; Space Physics
\\
In this paper we investigate the effects that an anomalous acceleration as
that experienced by the Pioneer spacecraft after they passed the 20 AU
threshold would induce on the orbital motions of the Solar System planets
placed at heliocentric distances of 20 AU or larger as Uranus, Neptune and
Pluto. It turns out that such an acceleration, with a magnitude of about 8 X
10^-10 m s^-2, would affect their orbits with secular and short-period signals
large enough to be detected with the present-day level of accuracy in orbit
determination. The absence of such anomalous signatures in the latest data
analyses rules out the possibility that in the region 20-40 AU of the Solar
System an anomalous force field inducing a constant and radial acceleration of
that size is present.
\\ ( http://arXiv.org/abs/gr-qc/0601055 , 36kb)
Posted by: mchan Jan 20 2006, 01:23 AM
QUOTE (AlexBlackwell @ Jan 5 2006, 09:56 AM)
Below is an excerpt from The Planetary Society's website of http://www.planetary.org/programs/projects/pioneer_anomaly/update_200511.html:
On using New Horizons to investigate the Pioneer Anomaly, here is a comment from a poster on sci.space.history --
begin quote
Unfortunately, New Horizons is a rotten design for this particular study,
even though it will be spin stabilized. The problem is that the RTG heat
will be radiated very unevenly. The Pioneer effect is equivalent to a few
tens of watts more being radiated antisunward than sunward. Pioneer was
quite good for this since the RTGs are on booms, and hence are radiating
mostly into free space. Still, one of the biggest questions is how much
IR bounces off the spacecraft, and which way it bounces.
On New Horizons, the RTG is very close to the spacecraft body, and radiating
a kW or so of IR, so hundreds of watts of IR will hit the spacecraft.
Figuring out where this will go exactly is very hard. The spacecraft is
very un-symmetrical in the direction of motion, so the IR reflections will
certainly favor some directions rather than others. Also, the spacecraft
is covered with thermal blankets, making reflections even harder to predict.
In general, the systematics are predicted to be several times the Pioneer
effect, and of an unknown magnitude. This was exactly the problem with
Cassini, which also had the RTGs mounted close in. (They spent a month
in cruise using only the reaction wheels, which is as good as spin stabilized,
and the measured acceleration was about 3x the Pioneer effect, and well
off the pre-flight predictions, and so was useless for studying this
effect. )
Lou Scheffer
end quote
Posted by: AlexBlackwell Jan 20 2006, 01:33 AM
QUOTE (mchan @ Jan 20 2006, 01:23 AM)
On using New Horizons to investigate the Pioneer Anomaly, here is a comment from a poster on sci.space.history --
[...]
Lou Scheffer
Well, Scheffer certainly has a "dog in the hunt." Go to the http://xxx.lanl.gov/ and run an "Author" search on Louis K. Scheffer.
Posted by: ljk4-1 Jan 20 2006, 03:09 PM
Will it be possible to design a KBO and/or Interstellar Medium probe that can "look" for the Pioneer Anomaly while still being able to properly explore the Kuiper Belt and beyond?
Cool as it would be, I cannot imagine anyone getting serious funding for a strictly PA mission at this stage.
Would would an "ideal" PA mission look like, anyway?
Posted by: ugordan Jan 20 2006, 03:12 PM
QUOTE (ljk4-1 @ Jan 20 2006, 04:09 PM)
Would would an "ideal" PA mission look like, anyway?
Probably a very long stick with an RTG at one end and a HGA at the other
Posted by: djellison Jan 20 2006, 03:30 PM
Pioneer 10 or 11 basically
Doug
Posted by: The Messenger Jan 20 2006, 03:57 PM
QUOTE (mchan @ Jan 19 2006, 06:23 PM)
On using New Horizons to investigate the Pioneer Anomaly, here is a comment from a poster on sci.space.history --
begin quote
...In general, the systematics are predicted to be several times the Pioneer
effect, and of an unknown magnitude. This was exactly the problem with
Cassini, which also had the RTGs mounted close in. (They spent a month
in cruise using only the reaction wheels, which is as good as spin stabilized,
and the measured acceleration was about 3x the Pioneer effect, and well
off the pre-flight predictions, and so was useless for studying this
effect. )
Lou Scheffer
end quote
Actually, this might be a significant and useful chunk of data, if the vector is known, and it is in either the same or opposite direction as the solar wind.
Amoung the possible explanations for the Pioneer enomally is a solar field effect that diminishes as i/r - which would be much more pronounced between 1 and 8 AU than >20. So a magnitude of three greater at closer distances is actually in-family. At distances greater than 20 AU, a 1/r attenuation reduces to a nearly constant rate, as observe by the Pioneer probes.
A higher magnitude effect in Cassini is consistent with the magnitude and attenuation of 'unmodeled forces' experienced by both Galileo and Ulysses. Since the effective 'force' of these peculiarities is in the same direction as the solar wind, it is impossible to disentangle the parameters. (Using the solar wind to model Galileo and Ulysses accelerations requires a secondary term that attenuates as 1/r. (According to Anderson & Nieto.)
Posted by: ljk4-1 Jan 20 2006, 04:24 PM
Paper: astro-ph/0601422
Date: Thu, 19 Jan 2006 10:51:50 GMT (4kb)
Title: Upper limits on density of dark matter in Solar system
Authors: I.B. Khriplovich and E.V. Pitjeva
Comments: 4 pages
\\
The analysis of the observational data for the secular perihelion precession
of Mercury, Earth, and Mars, based on the EPM2004 ephemerides, results in new
upper limits on density of dark matter in the Solar system.
\\ ( http://arXiv.org/abs/astro-ph/0601422 , 4kb)
Posted by: ljk4-1 Jan 20 2006, 06:50 PM
Paper: astro-ph/0601431
Date: Thu, 19 Jan 2006 17:08:29 GMT (79kb)
Title: Modified gravity without dark matter
Authors: R.H. Sanders
Comments: 28 pages, 10 figures, lecture given at Third Aegean Summer School,
The Invisible Universe: Dark Matter and Dark Energy
\\
On an empirical level, the most successful alternative to dark matter in
bound gravitational systems is the modified Newtonian dynamics, or MOND,
proposed by Milgrom. Here I discuss the attempts to formulate MOND as a
modification of General Relativity. I begin with a summary of the
phenomenological successes of MOND and then discuss the various covariant
theories that have been proposed as a basis for the idea. I show why these
proposals have led inevitably to a multi-field theory. I describe in some
detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and
discuss its successes and shortcomings. This lecture is primarily pedagogical
and directed to those with some, but not a deep, background in General
Relativity
\\ ( http://arXiv.org/abs/astro-ph/0601431 , 79kb)
Posted by: ljk4-1 Jan 20 2006, 07:13 PM
QUOTE (mchan @ Jan 19 2006, 08:23 PM)
On using New Horizons to investigate the Pioneer Anomaly, here is a comment from a poster on sci.space.history --
begin quote
Unfortunately, New Horizons is a rotten design for this particular study,
even though it will be spin stabilized. The problem is that the RTG heat
will be radiated very unevenly. The Pioneer effect is equivalent to a few
tens of watts more being radiated antisunward than sunward. Pioneer was
quite good for this since the RTGs are on booms, and hence are radiating
mostly into free space. Still, one of the biggest questions is how much
IR bounces off the spacecraft, and which way it bounces.
On New Horizons, the RTG is very close to the spacecraft body, and radiating
a kW or so of IR, so hundreds of watts of IR will hit the spacecraft.
Figuring out where this will go exactly is very hard. The spacecraft is
very un-symmetrical in the direction of motion, so the IR reflections will
certainly favor some directions rather than others. Also, the spacecraft
is covered with thermal blankets, making reflections even harder to predict.
In general, the systematics are predicted to be several times the Pioneer
effect, and of an unknown magnitude. This was exactly the problem with
Cassini, which also had the RTGs mounted close in. (They spent a month
in cruise using only the reaction wheels, which is as good as spin stabilized,
and the measured acceleration was about 3x the Pioneer effect, and well
off the pre-flight predictions, and so was useless for studying this
effect. )
Lou Scheffer
end quote
Why is it that the Pioneer and Voyager probes had to have their science instruments as far from the RTGs as possible, yet that does not seem to be the case with Cassini and New Horizons?
Better shielding? More advanced/protected instruments? We don't fear radiation as much as we used to?
Posted by: Borek Jan 20 2006, 08:20 PM
QUOTE (ljk4-1 @ Jan 20 2006, 07:13 PM)
Why is it that the Pioneer and Voyager probes had to have their science instruments as far from the RTGs as possible, yet that does not seem to be the case with Cassini and New Horizons?
Better shielding? More advanced/protected instruments? We don't fear radiation as much as we used to?
Well shielded RTG should radiate very little, shouldn't it?
Posted by: helvick Jan 20 2006, 09:02 PM
QUOTE (Borek @ Jan 20 2006, 09:20 PM)
Well shielded RTG should radiate very little, shouldn't it?
It will still radiate heat, the RTG itself isn't particularly efficient so most of the decay energy is ultimately expressed as heat which is radiated out (hence the kwatt or so referred to in the sci.space.history post) from the RTG module. A significant portion of this IR energy "hits" the main body of the spacecraft but is reflected away in arbitrary directions from it by the thermal insulation, hence the complexity of analysing the effect.
Posted by: The Messenger Jan 23 2006, 09:54 PM
QUOTE (Borek @ Jan 20 2006, 01:20 PM)
Well shielded RTG should radiate very little, shouldn't it?
The RTGs on the Pioneer probes were symetrically mounted on booms, so that the (waste) thermal energy should be symetrically distributed. One of the still plausible scenarios is that the solar wind has caused substantial aging or discoloration of the sun-facing side of the boom(s), causing the energy to be dispersed asymetrically.
This may sound like an absurdly small effect, but that it is the ballpark of the Pioneer anomalies (1x10^-9 m/s^2), and this is why it is so difficult to propose a definitive test - very, very small force.
Posted by: ljk4-1 Jan 23 2006, 10:44 PM
QUOTE (ljk4-1 @ Jan 18 2006, 10:30 AM)
Paper (*cross-listing*): gr-qc/0601055
Date: Sat, 14 Jan 2006 16:11:23 GMT (36kb)
Title: What do the orbital motions of the outer planets of the Solar System
tell us about the Pioneer Anomaly?
Authors: Lorenzo Iorio
Comments: Latex2e, 12 pages, 3 tables, 4 figures
Subj-class: General Relativity and Quantum Cosmology; Space Physics
\\
In this paper we investigate the effects that an anomalous acceleration as
that experienced by the Pioneer spacecraft after they passed the 20 AU
threshold would induce on the orbital motions of the Solar System planets
placed at heliocentric distances of 20 AU or larger as Uranus, Neptune and
Pluto. It turns out that such an acceleration, with a magnitude of about 8 X
10^-10 m s^-2, would affect their orbits with secular and short-period signals
large enough to be detected with the present-day level of accuracy in orbit
determination. The absence of such anomalous signatures in the latest data
analyses rules out the possibility that in the region 20-40 AU of the Solar
System an anomalous force field inducing a constant and radial acceleration of
that size is present.
\\ ( http://arXiv.org/abs/gr-qc/0601055 , 36kb)
Paper (*cross-listing*): gr-qc/0601055
replaced with revised version Fri, 20 Jan 2006 16:04:50 GMT (37kb)
Title: What do the orbital motions of the outer planets of the Solar System
tell us about the Pioneer anomaly?
Authors: Lorenzo Iorio
Comments: Latex2e, 13 pages, 3 tables, 4 figures, 14 references. References
added. Stressed the fact that, even by assuming errors in the planetary
orbital elements 30 times larger that those published by Pitjeva, the
anomalous Pioneer effects on Uranus, Neptune, Pluto still remain well larger
and, thus, detectable if present
Subj-class: General Relativity and Quantum Cosmology; Space Physics
\\ ( http://arXiv.org/abs/gr-qc/0601055 , 37kb)
Posted by: The Messenger Jan 24 2006, 03:17 PM
QUOTE (ljk4-1 @ Jan 23 2006, 03:44 PM)
Title: What do the orbital motions of the outer planets of the Solar System
tell us about the Pioneer anomaly?
Authors: Lorenzo Iorio
Comments: ... Stressed the fact that, even by assuming errors in the planetary
orbital elements 30 times larger that those published by Pitjeva, the
anomalous Pioneer effects on Uranus, Neptune, Pluto still remain well larger
and, thus, detectable if present
...
This is an important constraint, under the tested conditions:
QUOTE (Iorio)
In particular, we will investigate the possibility that an external, unknown constant and uniform force field inducing an acceleration of (8)×10−10 m s−2 on a test particle is present in the outer regions of the Solar System within 20-40 AU.
I think this highly constrains MOND-like, Dark Matter-like, or Dark Energy-like candidates.
These results do not constrain 1) non-linear effects, 2) systemics that may cause us to incorrectly calculate the mass and/or positions of the planets, or 3) linear effects that only act upon small conductive, and/or radioactive bodies.
Although the measured Pioneer accelerations appear to be roughly linear, it is important to remember that over great distances: 1/r, 1/r^2 and 1/z^4 - these normal distant field scaling factors can be reduced to nearly linear approximations (over relatively short distances)
Posted by: Mongo Jan 24 2006, 06:16 PM
QUOTE (The Messenger @ Jan 24 2006, 03:17 PM)
These results do not constrain 1) non-linear effects, 2) systemics that may cause us to incorrectly calculate the mass and/or positions of the planets, or 3) linear effects that only act upon small conductive, and/or radioactive bodies.
I wonder if the magnitude of the 'Pioneer Effect' depends upon the radial velocity of the object, such that objects moving away from the Sun appear to have a force acting upon them toward the Sun, and objects moving toward the Sun appear to have a force acting upon them away from the Sun, with the magnitude of the 'force' proportional to the radial velocity of the object.
Objects in bound orbits, such as the planets, would end up having the two effects cancel out over each full orbit. The effect of such a 'force' would be to make their orbits somewhat less eccentric than they would otherwise be, but since the effect would be small (due to the low eccentricity of all the large objects with well-known orbits, resulting in low radial velocities) and would act over only half of an orbital cycle before being reversed (as the radial velocity changes from outward to inward and vice versa), the difference between the actual orbit, forced to lower eccentricity under the Pioneer Effect, and a non-Pioneer Effect orbit of sufficiently lower eccentricty to match, might well be too small to observe with current technology.
The 'Pioneer Effect' would only be easily visible in unbound trajectories such as Pioneers 10 and 11, where the effect is larger due to the larger radial velocity, and can accumulate over a much longer period of time.
Bill
Posted by: hal_9000 Jan 26 2006, 07:30 PM
From New Scientist -> http://www.newscientistspace.com/article.ns?id=dn8631
Gravity theory dispenses with dark matter
A modified theory of gravity that incorporates quantum effects can explain a trio of puzzling astronomical observations – including the wayward motion of the Pioneer spacecraft in our solar system, new studies claim.
The work appears to rule out the need to invoke dark matter or another alternative gravity theory called MOND (Modified Newtonian Dynamics). But other experts caution it has yet to pass the most crucial test – how to account for the afterglow of the big bang.
Astronomers realised in the 1970s that the gravity of visible matter alone was not enough to prevent the fast-moving stars and gas in spiral galaxies from flying out into space. They attributed the extra pull to a mysterious substance called dark matter, which is now thought to outweigh normal matter in the universe by 6 to 1.
But researchers still do not know what dark matter actually is, and some have come up with new theories of gravity to explain the galaxy observations. MOND, for example, holds that there are two forms of gravity.
Above a certain acceleration, called a0, objects move according to the conventional form of gravity, whose effects weaken as two bodies move further apart in proportion to the square of distance. But below a0, objects are controlled by another type of gravity that fades more slowly, decreasing linearly with distance.
But critics point out that MOND cannot explain the observed masses of clusters of galaxies without invoking dark matter, in the form of almost massless, known particles called neutrinos.
http://www.newscientistspace.com/article.ns?id=dn8631
Posted by: Jeff7 Jan 27 2006, 01:41 AM
QUOTE (hal_9000 @ Jan 26 2006, 02:30 PM)
From New Scientist -> http://www.newscientistspace.com/article.ns?id=dn8631
Gravity theory dispenses with dark matter
Sounds like a version of the theory that general relativity needs to be applied to gravitational models, instead of simpler Newtonian physics. That theory hclaims to be able to do away with dark matter entirely and
still explain both small-scale and very large-scale systems.
I just imagine the thought of doing away with dark matter is unappealing to some people, as I'm sure some have made the study of dark matter their life's work. Another way of looking at it though is that they're just inadvertently referring to "the effects of general relativity" as "dark matter".
Posted by: ljk4-1 Jan 27 2006, 06:34 PM
Paper: astro-ph/0601581
Date: Wed, 25 Jan 2006 21:28:29 GMT (15kb)
Title: Globular Clusters as a Test for Gravity in the Weak Acceleration Regime
Authors: Riccardo Scarpa, Gianni Marconi, and Roberto Gilmozzi
Comments: Comments: To Appear in the proceeding of the "First crisis in
cosmology" conference, published in the American Institute of Physiscs'
proceedings series, Vol. 822. (includes 3 pages and 1 fig)
\\
Non-baryonic Dark Matter (DM) appears in galaxies and other cosmic structures
when and only when the acceleration of gravity, as computed considering only
baryons, goes below a well defined value a0=1.2e-8 cm/s/s. This might indicate
a breakdown of Newton's law of gravity (or inertia) below a0, an acceleration
smaller than the smallest probed in the solar system. It is therefore important
to verify whether Newton's law of gravity holds in this regime of
accelerations. In order to do this, one has to study the dynamics of objects
that do not contain significant amounts of DM and therefore should follow
Newton's prediction for whatever small accelerations. Globular clusters are
believed, even by strong supporters of DM, to contain negligible amounts of DM
and therefore are ideal for testing Newtonian dynamics in the low acceleration
limit. Here, we discuss the status of an ongoing program aimed to do this test.
Compared to other studies of globular clsuters, the novelty is that we trace
the velocity dispersion profile of globular clusters far enough from the center
to probe gravitational accelerations well below a0. In all three clusters
studied so far the velocity dispersion is found to remain constant at large
radii rather than follow the Keplerian falloff. On average, the flattening
occurs at the radius where the cluster internal acceleration of gravity is
1.8+-0.4 x 10^{-8} cm/s/s, fully consistent with MOND predictions.
\\ ( http://arXiv.org/abs/astro-ph/0601581 , 15kb)
Posted by: ljk4-1 Feb 1 2006, 04:02 AM
From The Planetary Society update:
Our strategy for the upcoming analysis of the newly available data can be summed up as follows: First, studying the early mission data may help us unambiguously determine whether the acceleration points towards the Earth, the Sun, or some other direction. Second, we hope to find out how the anomaly begins or if it was present throughout the mission. Third, we hope to be able to determine how this anomalous acceleration changed over time. Fourth, we will compare data from the two Pioneers to see if we can discern any notable differences in their behavior. Lastly, we will use the MDRs to develop a better engineering model of the spacecraft, making use, for instance, of finite element analysis methods to understand its thermal behavior.
In March 2006, for the very last time the Earth will be in a favorable position to receive Pioneer 10's radio signal. It is possible that Pioneer 10 is still able to transmit, despite the age of its electronics, the extreme coldness of deep space, and the diminishing amount of electrical power on board. The possibility that the Deep Space Network will attempt to reacquire Pioneer 10's weak signal is currently being investigated, raising the hope, however faint, that we may yet have another data point to aid in our investigation of the Pioneers' enigmatic behavior.
The rest is here:
http://planetary.org/programs/projects/pioneer_anomaly/update_200601.html
Posted by: Richard Trigaux Feb 1 2006, 08:27 AM
QUOTE (ljk4-1 @ Feb 1 2006, 04:02 AM)
From The Planetary Society update:
Our strategy for the upcoming analysis of the newly available data ...
The rest is here:
http://planetary.org/programs/projects/pioneer_anomaly/update_200601.html
So this data was recovered and is now safe. Good move. Now serious work can begin.
Posted by: The Messenger Feb 1 2006, 03:54 PM
QUOTE (Richard Trigaux @ Feb 1 2006, 01:27 AM)
So this data was recovered and is now safe. Good move. Now serious work can begin.
It is an extremely difficult and tedious proposition. Each operation of a thruster must be accounted for, and every encounter with a third body - a moon, a planet, and a planetary system requires accurate mass and distance estimates.
It will be interesting to see if the Pioneer probe data pans out in the lower orbits like Cassini, Galileo, and Ulysses. Each of these probes experienced, (or rather, accelerations were measured), that exceed the 'Pioneer' effect by at least one magnitude, however, it is not possible to untangle the measured acceleration from the solar wind: It is in the same direction. (I think this measured anomally in Galileo and Ulysses is also in the opposite direction from the Pioneer probe acceleration - I don't have any numbers, other than a magnitude for Cassini.)
We will be lucky if we can hear from Pioneer in March, but if I remember correctly, the probe is no longer executing commands, so it may not be possible to enter the Doppler-repeater mode necessary for accurate distant measurements. (In this mode, the Pioneer probes echoed back an ultrastable signal sent from the Earth a harmonic frequency. If we are only listening to the Pioneer transmitter, there is not sufficent accuracy in the on-board timing to obtain accurate distance estimates.)
Posted by: Richard Trigaux Feb 2 2006, 09:54 AM
QUOTE (The Messenger @ Feb 1 2006, 03:54 PM)
We will be lucky if we can hear from Pioneer in March, but if I remember correctly, the probe is no longer executing commands,
Why the probe is no longer executing commands? if it is because the power it receives is too weak, it would be worth using a large radio transmitter, such as Arecibo. Obtaining a last point of Pioneer effect is worth some seconds of Arecibo I think
Posted by: Richard Trigaux Feb 2 2006, 09:56 AM
QUOTE (The Messenger @ Feb 1 2006, 03:54 PM)
It will be interesting to see if the Pioneer probe data pans out in the lower orbits like Cassini, Galileo, and Ulysses. Each of these probes experienced, (or rather, accelerations were measured), that exceed the 'Pioneer' effect by at least one magnitude, however, it is not possible to untangle the measured acceleration from the solar wind: It is in the same direction. (I think this measured anomally in Galileo and Ulysses is also in the opposite direction from the Pioneer probe acceleration - I don't have any numbers, other than a magnitude for Cassini.)
It is not sure at all that the solar wind has a constant amplitude (speed, density, directio) everywhere. Especially it could be weaker out of the ecliptic,and eventually very variable. Ulysse data should tell us.
Posted by: ugordan Feb 2 2006, 12:05 PM
QUOTE (Richard Trigaux @ Feb 2 2006, 10:54 AM)
Why the probe is no longer executing commands? if it is because the power it receives is too weak, it would be worth using a large radio transmitter, such as Arecibo. Obtaining a last point of Pioneer effect is worth some seconds of Arecibo I think
It doesn't have to execute commands at all. All we need is detection of its carrier signal to measure the Doppler effect.
QUOTE (Richard Trigaux)
It is not sure at all that the solar wind has a constant amplitude (speed, density, directio) everywhere. Especially it could be weaker out of the ecliptic,and eventually very variable. Ulysse data should tell us.
It's a constant misconception/mixup that the solar wind is pushing on these probes. While to some extent you might say a force is being felt, a few particles per cubic cm hardly amount to much.
In reality, solar
light pressure is the culprit in exerting quite measurable forces and torques on the spacecraft.
The same goes for a solar sail, it doesn't really ride on solar wind, but on light from the sun.
Posted by: The Messenger Feb 2 2006, 05:04 PM
QUOTE (ugordan @ Feb 2 2006, 05:05 AM)
It doesn't have to execute commands at all. All we need is detection of its carrier signal to measure the Doppler effect.
Measuring the carrier would give us the velocity, but not the distance, and the probes native carrier is much too unstable to gain an accurate reading of the velocity.
In the 'repeater' mode, the Pioneer probes would listen to a frequency from earth, then rebroadcast the same pattern at a frequency multiple. Since the ultrastable signal from Earth controls the oscillator, both timing elements are known with great precision.
QUOTE
It's a constant misconception/mixup that the solar wind is pushing on these probes. While to some extent you might say a force is being felt, a few particles per cubic cm hardly amount to much.
In reality, solar
light pressure is the culprit in exerting quite measurable forces and torques on the spacecraft.
The same goes for a solar sail, it doesn't really ride on solar wind, but on light from the sun.
True, but the thermal effect is a little easier to model that the solar wind - for one thing, the particles in the solar wind may contain any charge, and this charge may either attract or repel the craft upon impact.
On both Ulysses and Galilio, Anderson & Co. had to use an unexpected solar vector to model the Solar wind effects, and a similar deviation was noticed in Cassini. The polarity of these vectors near Jupiter is opposite of what I stated earlier; that is, the apparent acceleration is towards the sun, just like Pioneer.
In any case, the PI's do not consider solar wind or heating effects to be primary candidates. A very comprehensive treatment of the problem can be found in:
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf
QUOTE (Anderson-etal)
Currently, we find no mechanism or theory that explains the anomalous acceleration. What we can say with some confidence is that the anomalous acceleration is a line of sight constant acceleration of the spacecraft toward the Sun.
Even though fits to the Pioneers appear to match the noise level of the data, in reality the fit levels are as much as 50 times above the fundamental
noise limit of the data.
Until more is known, we must admit that the most likely cause of this effect is an unknown systematic. (We ourselves are divided as to whether “gas leaks” or “heat” is this “most likely cause.”)
The arguments for “gas leaks” are: i) All spacecraft experience a gas leakage at some level. ii) There is enough gas available to cause the effect. iii) Gas leaks require not new physics. However, iv) it is unlikely that the two Pioneer spacecraft would have gas leaks at similar rates, over the entire data interval, especially then the valves have been used for so many maneuvers... v) Most importantly, it would require that these gas leaks be precisely pointed towards the front of the spacecraft so as not to cause a large spin-rate changes. But vi) it could still be true anyway.
The main arguments for “heat” are: i) There is so much heat available that a small amount of the total could cause the effect. ii) In deep space the spacecraft will be in approximate thermal equilibrium. The heat should then be emitted at an approximately constant rate, deviating from a constant only because of the slow exponential decay of the Plutonium heat source. It is hard to resist the notion that this heat somehow must be the origin of the effect. However, iii) there is no solid explanation in hand as to how a specific heat mechanism could work. Further, iv) the decrease in the heat supply over time should have been seen by now.
...
Finally, we observe that if no convincing explanation is to be obtained, the possibility remains that the effect is real. It could even be related to cosmological quantities, as has been intimated...This possibility necessitates a cautionary note on phenomenology: At this point in time, with the limited results available, there is a phenomenological equivalence between the [standard] and [alternative] points of view. But somehow, the choice one makes affects one’s outlook and direction of attack. If one has to consider new physics one should be open to both points of view. In the unlikely event that there is new physics, one does not want to miss it because one had the wrong mind set.
Posted by: ljk4-1 Feb 2 2006, 05:07 PM
Any chance there is a foreign object like a small meteoroid that impacted and stuck onto the Pioneer probes that may be affecting things?
Posted by: Richard Trigaux Feb 2 2006, 06:49 PM
QUOTE (ljk4-1 @ Feb 2 2006, 05:07 PM)
Any chance there is a foreign object like a small meteoroid that impacted and stuck onto the Pioneer probes that may be affecting things?
if it had an effect such as removing a part of the structure, it may change the thermal model in the way it receives thrust from solar light. But more likely many dust did not produced large break-up, but many pin-holes which change the thermal property, in a way similar for all the probes. (Or in a different way, as there may be seasons for interplanetary dust).
Posted by: The Messenger Feb 2 2006, 07:04 PM
QUOTE (ljk4-1 @ Feb 2 2006, 10:07 AM)
Any chance there is a foreign object like a small meteoroid that impacted and stuck onto the Pioneer probes that may be affecting things?
Very unlikely. The two Pioneer probes are moving in nearly opposite directions, and we are talking about a constant acceleration towards the sun, not a one-time change in a velocity vector. So unless microparticle bombardment is both uniform and omni-directional, this can all-but be ruled out.
Another interesting observation: The Viking probes are losing power at a slower rate than nuclear theory predicts. Currently, the only explanation for this is an increase in the efficiency of the thermalcouples converting nuclear energy into electrical energy as the temperature decreases. (This is an expected improvement, but apparently the magnitude of improvement is greater-than-expected.)
Contact with Pioneer 10 should give us another data point concerning this thermal efficiency phenomenon. While unexpected quantum efficiency in an ultra-cold environment may be a factor, we cannot rule out the possibility that the nuclear decay efficiency and/or rate is an extremely weak function of the radiative and/or the gravimetric environment.
Posted by: ljk4-1 Feb 8 2006, 03:26 PM
Astrophysics, abstract
astro-ph/0602161
From: R. H. Sanders [view email]
Date: Tue, 7 Feb 2006 16:51:22 GMT (43kb)
Solar system constraints on multi-field theories of modified dynamics
Authors: R.H. Sanders
Comments: 10 pages, 5 figures, submitted MNRAS
Any viable theory of modified Newtonian dynamcs (MOND) as modified gravity is likely to require fields in addition to the usual tensor field of General Relativity. For such theories the MOND phenomenology emerges from an effective fifth force probably associated with a scalar field. Here I consider the constraints imposed upon such theories by solar system phenomenology, primarily by the absence of significant deviations from inverse square attraction in the inner solar system as well as detectable local preferred frame effects. The current examples of multi-field theories can be constructed to satisfy these constraints and such theories lead inevitably to an anomalous non inverse-square force in the outer solar system.
http://arxiv.org/abs/astro-ph/0602161
Posted by: AlexBlackwell Feb 9 2006, 12:11 AM
I'm surprised that you haven't mentioned this one yet, ljk4-1
Planetary Radio had an interview with JPL's John Anderson on February 6, 2006:
http://planetary.org/radio/show/00000154/.
Under a category similar to "DVD Extras": Emily Lakdawalla and Bruce Betts.
Posted by: ljk4-1 Feb 9 2006, 12:13 AM
QUOTE (AlexBlackwell @ Feb 8 2006, 07:11 PM)
I'm surprised that you haven't mentioned this one yet, ljk4-1
Planetary Radio had an interview with JPL's John Anderson on February 6, 2006:
http://planetary.org/radio/show/00000154/.
Under a category similar to "DVD Extras": Emily Lakdawalla and Bruce Betts.
The signal was too weak for me to detect.
Thanks for catching that one.
Posted by: ljk4-1 Feb 9 2006, 04:19 PM
General Relativity and Quantum Cosmology, abstract
gr-qc/0509021
From: Andreas Rathke [view email]
Date: Wed, 7 Sep 2005 12:45:40 GMT (259kb)
Pioneer anomaly: What can we learn from LISA?
Authors: Denis Defrere, Andreas Rathke
Comments: 19 pages, 4 figures. Talk given by D. Defrere at the conference "Lasers, Clocks, and Drag-Free", ZARM, Bremen, Germany, 30 May - 1 June 2005
The Doppler tracking data from two deep-space spacecraft, Pioneer 10 and 11, show an anomalous blueshift, which has been dubbed the "Pioneer anomaly". The effect is most commonly interpreted as a real deceleration of the spacecraft - an interpretation that faces serious challenges from planetary ephemerides. The Pioneer anomaly could as well indicate an unknown effect on the radio signal itself. Several authors have made suggestions how such a blueshift could be related to cosmology. We consider this interpretation of the Pioneer anomaly and study the impact of an anomalous blueshift on the Laser Interferometer Space Antenna (LISA), a planned joint ESA-NASA mission aiming at the detection of gravitational waves. The relative frequency shift (proportional to the light travel time) for the LISA arm length is estimated to 10E-16, which is much bigger than the expected amplitude of gravitational waves. The anomalous blueshift enters the LISA signal in two ways, as a small term folded with the gravitational wave signal, and as larger term at low frequencies. A detail analysis shows that both contributions remain undetectable and do not impair the gravitational-wave detection.
This suggests that the Pioneer anomaly will have to be tested in the outer Solar system regardless if the effect is caused by an anomalous blueshift or by a real force.
http://arxiv.org/abs/gr-qc/0509021
Posted by: ljk4-1 Feb 9 2006, 04:29 PM
General Relativity and Quantum Cosmology, abstract
gr-qc/0602003
From: Antonio F. Ranada [view email]
Date: Wed, 1 Feb 2006 15:30:16 GMT (10kb)
A model for the Pioneer Anomaly
Authors: Antonio F. Ranada, Alfredo Tiemblo
Comments: 11 pages, no figures
We propose an explanation to the Pioneer Anomaly, the anomalous blueshift in the radio signals from the Pioneer 10/11 spacecrafts that remains unexplained 30 years after being discovered by a NASA team around 1975. It was detected as a Doppler shift that does not correspond to any known motion of the ships. In 1998, after many unsuccessful efforts to account for it, the discoverers suggested "the possibility that the origin of the anomalous signal is new physics".
We show here that the phenomenon has the same observational footprint as an acceleration of the atomic clocks time with respect to the astronomical time.
Surprisingly, this curious new idea turns out to be compatible with current physics; lacking a unified theory of quantum physics and gravitation, we cannot discard it a priori.
We expound a mechanism that produces such an acceleration as a result of the coupling of the background gravitation and the quantum vacuum. This suggests a solution to the riddle, in which the velocity of a receding ship, as deduced from the Doppler effect, is smaller than the value predicted by the standard theory of gravitation.
We conclude that the Pioneer Anomaly is probably the signature of the difference between the marches of the astronomical clock of the orbit and the atomic clock inside the ship.
http://arxiv.org/abs/gr-qc/0602003
Posted by: ljk4-1 Feb 10 2006, 10:28 PM
Quotes from the article "Listening for Pioneer 10":
Centauri Dreams is following the Pioneer 10 story with great interest, and not just in terms of the anomalous effects that continue to keep this mission in the news. Ponder that Pioneer 10 was launched in 1972 and consider that even with the technologies of its day, the probe may still be able to communicate with Earth.
We have learned so much in the interim about hardened electronics and autonomous self-repair that there is reason to believe probes to even remoter locations in the Kuiper Belt and beyond are feasible providing we can solve the propulsion conundrum.
...
It’s too late for New Horizons, of course, but any followup Pluto/Kuiper Belt mission would have such an opportunity. On that score, see T. Bondo, R. Walker, A. Rathke et al., “Preliminary Design of an Advanced Mission to Pluto,” scheduled to appear in the proceedings of the 24th International Symposium on Space Technology and Science, Miyazaki, Japan, June 2006, and already available online (PDF warning).
http://www.centauri-dreams.org/?p=534
Posted by: The Messenger Feb 13 2006, 11:11 PM
QUOTE (ljk4-1 @ Feb 9 2006, 09:29 AM)
General Relativity and Quantum Cosmology, abstract
gr-qc/0602003
From: Antonio F. Ranada [view email]
Date: Wed, 1 Feb 2006 15:30:16 GMT (10kb)
A model for the Pioneer Anomaly
Authors: Antonio F. Ranada, Alfredo Tiemblo
Comments: 11 pages, no figures
We propose an explanation to the Pioneer Anomaly, the anomalous blueshift in the radio signals from the Pioneer 10/11 spacecrafts that remains unexplained 30 years after being discovered by a NASA team around 1975. It was detected as a Doppler shift that does not correspond to any known motion of the ships. In 1998, after many unsuccessful efforts to account for it, the discoverers suggested "the possibility that the origin of the anomalous signal is new physics".
We show here that the phenomenon has the same observational footprint as an acceleration of the atomic clocks time with respect to the astronomical time...
http://arxiv.org/abs/gr-qc/0602003
...It also has the same observational footprint as an increase in the speed of light with increasing distance from the center of mass. A family of observations that don't fit the mold could be a clue that all is not well in the beeg peekture.
Posted by: ljk4-1 Feb 14 2006, 06:13 PM
Astrophysics, abstract
astro-ph/0602266
From: Joao Magueijo [view email]
Date: Sun, 12 Feb 2006 20:46:43 GMT (240kb)
MOND habitats within the solar system
Authors: Jacob Bekenstein, Joao Magueijo
MOdified Newtonian Dynamics (MOND) is an interesting alternative to dark matter in extragalactic systems. We here examine the possibility that mild or even strong MOND behavior may become evident well inside the solar system, in particular near saddle points of the total gravitational potential. Whereas in Newtonian theory tidal stresses are finite at saddle points, they are expected to diverge in MOND, and to remain distinctly large inside a sizeable oblate ellipsoid around the saddle point. We work out the MOND effects using the nonrelativistic limit of the T$e$V$e$S theory, both in the perturbative nearly Newtonian regime and in the deep MOND regime. While strong MOND behavior would be a spectacular ``backyard'' vindication of the theory, pinpointing the MOND-bubbles in the setting of the realistic solar system may be difficult.
Space missions, such as the LISA Pathfinder, equipped with sensitive accelerometers, may be able to explore the larger perturbative region.
http://arxiv.org/abs/astro-ph/0602266
Posted by: ljk4-1 Feb 14 2006, 06:30 PM
QUOTE (ljk4-1 @ Jan 13 2006, 09:44 AM)
I don't want this turning into the Dark Matter/Energy Topic (unless of course that is what is affecting the Pioneer probes), but I wanted to share this news item while we are still on the subject:
Dark Matter Galaxy?
Summary - (Thu, 12 Jan 2006) Astronomers think they might have found a "dark galaxy", that has no stars and emits no light. Although the galaxy itself, located 50 million light years from Earth, is practically invisible, it contains a small amount of neutral hydrogen which emits radio waves. If astronomers are correct, this galaxy contains ten billion times the mass of Sun, but only 1% of this is hydrogen - the rest is dark matter.
http://www.universetoday.com/am/publish/pparc_darkmatter_virgohi.html?1212006
If there is life in that galaxy, just try to imagine how utterly different it probably is from ours.
Astrophysics, abstract
astro-ph/0602271
From: Galina Korotkova Gennadievna [view email]
Date: Mon, 13 Feb 2006 08:03:04 GMT (90kb)
Disturbed isolated galaxies: indicators of a dark galaxy population?
Authors: I.D.Karachentsev, V.E.Karachentseva, W.K.Huchtmeier
Comments: 5 pages, 1 figure. Astronomy and Astrophysics, accepted
We report the results of our search for disturbed (interacting) objects among very isolated galaxies. The inspections of 1050 northern isolated galaxies from KIG and 500 nearby, very isolated galaxies situated in the Local Supercluster yielded five and four strongly disturbed galaxies, respectively. We suggest that the existence of "dark" galaxies explains the observed signs of interaction. This assumption leads to a cosmic abundance of dark galaxies (with the typical masses for luminous galaxies) that is less than ~1/20 the population of visible galaxies.
http://arxiv.org/abs/astro-ph/0602271
Posted by: ljk4-1 Feb 14 2006, 07:03 PM
General Relativity and Quantum Cosmology, abstract
gr-qc/0601055
From: Lorenzo Iorio [view email]
Date (v1): Sat, 14 Jan 2006 16:11:23 GMT (36kb)
Date (revised v2): Fri, 20 Jan 2006 16:04:50 GMT (37kb)
Date (revised v3): Mon, 13 Feb 2006 16:40:21 GMT (38kb)
What do the orbital motions of the outer planets of the Solar System tell us about the Pioneer anomaly?
Authors: Lorenzo Iorio
Comments: Latex2e, 13 pages, 3 tables, 4 figures, 15 references. Reference added. Stressed the fact that, even by assuming errors in the planetary orbital elements 30 times larger that those published by Pitjeva, the anomalous Pioneer effects on Uranus, Neptune, Pluto still remain well larger and, thus, detectable if present. Small corrections to the numerical values of Table 1 and Table 3: conclusions unchanged
Subj-class: General Relativity and Quantum Cosmology; Space Physics
In this paper we investigate the effects that an anomalous acceleration as that experienced by the Pioneer spacecraft after they passed the 20 AU threshold would induce on the orbital motions of the Solar System planets placed at heliocentric distances of 20 AU or larger as Uranus, Neptune and Pluto. It turns out that such an acceleration, with a magnitude of about 8 X 10^-10 m s^-2, would affect their orbits with secular and short-period signals large enough to be detected with the present-day level of accuracy in orbit determination. The absence of such anomalous signatures in the latest data analyses rules out the possibility that in the region 20-40 AU of the Solar System an anomalous force field inducing a constant and radial acceleration of that size is present.
http://arxiv.org/abs/gr-qc/0601055
Posted by: ljk4-1 Feb 23 2006, 07:01 PM
General Relativity and Quantum Cosmology, abstract
gr-qc/0602089
From: Kjell Tangen [view email]
Date: Wed, 22 Feb 2006 15:35:17 GMT (92kb)
Could the Pioneer anomaly have a gravitational origin?
Authors: Kjell Tangen
Comments: 9 pages, 1 figure
If the Pioneer anomaly has a gravitational origin, it would, according to the equivalence principle, distort the motions of the planets in the Solar System. Since no anomalous motion of the planets have been detected, it is generally believed that the Pioneer anomaly can not originate from a gravitational source in the Solar System. However, this conclusion becomes less obvious when considering models that either imply modifications to gravity at long range or gravitational sources localized to the outer Solar System, given the uncertainty in the orbital parameters of the outer planets. Following the general assumption that the Pioneer spacecrafts move geodesically in a spherically symmetric spacetime metric, we derive the metric disturbance that is needed in order to account for the Pioneer anomaly. We then analyze the residual effects on the astronomical observables of the outer planets that would arise from this metric disturbance, given an arbitrary metric theory of gravity. The computed residuals are much larger than the observed residuals, and we are lead to the conclusion that the Pioneer anomaly can not originate from a metric disturbance and therefore that the motion of the Pioneer spacecrafts must be non-geodesic. Since our results are model independent, they can be applied to rule out any model of the Pioneer anomaly that implies that the Pioneer spacecrafts move geodesically in a perturbed spacetime metric, regardless of the origin of this metric disturbance.
http://arxiv.org/abs/gr-qc/0602089
Posted by: ljk4-1 Mar 22 2006, 04:26 PM
General Relativity and Quantum Cosmology, abstract
gr-qc/0511026
From: J. R. Brownstein [view email]
Date (v1): Sun, 6 Nov 2005 02:40:04 GMT (162kb)
Date (revised v2): Fri, 17 Mar 2006 19:20:20 GMT (29kb)
Date (revised v3): Fri, 17 Mar 2006 21:22:19 GMT (29kb)
Gravitational solution to the Pioneer 10/11 anomaly
Authors: J. R. Brownstein, J. W. Moffat
Comments: 12 pages, 3 figures, 2 tables. Accepted for publication in Classical and Quantum Gravity, March 17, 2006
A fully relativistic modified gravitational theory including a fifth force skew symmetric field is fitted to the Pioneer 10/11 anomalous acceleration. The theory allows for a variation with distance scales of the gravitational constant G, the fifth force skew symmetric field coupling strength omega and the mass of the skew symmetric field mu=1/lambda. A fit to the available anomalous acceleration data for the Pioneer 10/11 spacecraft is obtained for a phenomenological representation of the "running" constants and values of the associated parameters are shown to exist that are consistent with fifth force experimental bounds. The fit to the acceleration data is consistent with all current satellite, laser ranging and observations for the inner planets.
http://arxiv.org/abs/gr-qc/0511026
Posted by: The Messenger Mar 22 2006, 05:08 PM
QUOTE (ljk4-1 @ Mar 22 2006, 09:26 AM)
General Relativity and Quantum Cosmology, abstract
gr-qc/0511026
From: J. R. Brownstein [view email]
Date (v1): Sun, 6 Nov 2005 02:40:04 GMT (162kb)
Date (revised v2): Fri, 17 Mar 2006 19:20:20 GMT (29kb)
Date (revised v3): Fri, 17 Mar 2006 21:22:19 GMT (29kb)
Gravitational solution to the Pioneer 10/11 anomaly
Authors: J. R. Brownstein, J. W. Moffat
Comments: 12 pages, 3 figures, 2 tables. Accepted for publication in Classical and Quantum Gravity, March 17, 2006
A fully relativistic modified gravitational theory including a fifth force skew symmetric field is fitted to the Pioneer 10/11 anomalous acceleration. The theory allows for a variation with distance scales of the gravitational constant G, the fifth force skew symmetric field coupling strength omega and the mass of the skew symmetric field mu=1/lambda. A fit to the available anomalous acceleration data for the Pioneer 10/11 spacecraft is obtained for a phenomenological representation of the "running" constants and values of the associated parameters are shown to exist that are consistent with fifth force experimental bounds. The fit to the acceleration data is consistent with all current satellite, laser ranging and observations for the inner planets.
http://arxiv.org/abs/gr-qc/0511026
The Tangen and Iorio papers place real constraints upon odd-ball gravitmetric theories which could have accounted for the Pioneer anomaly. This paper is just an exercise in curve fitting. Introducing distant forces that suddenly appear, as needed, to explain observations, is better left to Hobbitary universes. No more dark stuff, please.
Posted by: ljk4-1 Mar 28 2006, 06:05 PM
Astrophysics, abstract
astro-ph/0502582
From: Michael Makoid . D. [view email]
Date (v1): Mon, 28 Feb 2005 16:46:47 GMT (362kb)
Date (revised v2): Sat, 25 Mar 2006 16:33:55 GMT (368kb)
Ab Initio Calculation of the Anomalous Acceleration of Pioneer 10 In Vacuo
Authors: Russell Anania, Michael Makoid (Creighton University, Omaha, NE.)
Comments: 16 pages with two jpeg figures
The anomalous acceleration of Pioneer 10 is presented as a calculation using a simple optical model. The model is based on the bending of background gravity behind the Sun in the same way that light is bent by the Sun. Structures of ponderable matter about the Solar system, neutron stars, and galaxies are described. Viewable red and blue shiftings of light are predicted.
http://arxiv.org/abs/astro-ph/0502582
Posted by: The Messenger Mar 28 2006, 07:44 PM
QUOTE (ljk4-1 @ Mar 28 2006, 11:05 AM)
Astrophysics, abstract
astro-ph/0502582
Authors: Russell Anania, Michael Makoid (Creighton University, Omaha, NE.)
The anomalous acceleration of Pioneer 10 is presented as a calculation using a simple optical model. The model is based on the bending of background gravity behind the Sun in the same way that light is bent by the Sun. Structures of ponderable matter about the Solar system, neutron stars, and galaxies are described. Viewable red and blue shiftings of light are predicted.
http://arxiv.org/abs/astro-ph/0502582
What we are talking about here is matter behaving as if there is a optical density assignable to free space space that is a function of mass - many times greater than predicted by GR
What these two have failed to evaluate, is the effect such a gravitational gradient would have upon the orbits (or the predicted masses) of the planets
Posted by: ljk4-1 Mar 30 2006, 03:09 PM
Astrophysics, abstract
astro-ph/0603790
From: Ettore Minguzzi [view email]
Date: Wed, 29 Mar 2006 14:44:25 GMT (8kb)
Possible relation between galactic flat rotational curves and the Pioneers' anomalous acceleration
Authors: E. Minguzzi
Comments: Latex2e, 6 pages, no figures
We consider a generic minimal modification of the Newtonian potential, that is a modification that introduces only one additional dimensional parameter. The modified potential depends on a function whose behavior for large and small distances can be fixed in order to obtain respectively (i) galactic flat rotational curves and (ii) a universal constant acceleration independent of the masses of the interacting bodies (Pioneer anomaly). Then using a dimensional argument we show that the Tully-Fisher relation for the maximal rotational velocity of spiral galaxies follows without any further assumptions. This result suggests that the Pioneer anomalous acceleration and the flat rotational curves of galaxies could have a common origin in a modified gravitational theory. The relation of these results with the Modified Newtonian Dynamics (MOND) is discussed.
http://arxiv.org/abs/astro-ph/0603790
Posted by: ljk4-1 Apr 4 2006, 04:26 PM
General Relativity and Quantum Cosmology, abstract
gr-qc/0601055
From: Lorenzo Iorio [view email]
Date (v1): Sat, 14 Jan 2006 16:11:23 GMT (36kb)
Date (revised v2): Fri, 20 Jan 2006 16:04:50 GMT (37kb)
Date (revised v3): Mon, 13 Feb 2006 16:40:21 GMT (38kb)
Date (revised v4): Sat, 1 Apr 2006 15:06:33 GMT (79kb)
What do the orbital motions of the outer planets of the Solar System tell us about the Pioneer anomaly?
Authors: Lorenzo Iorio, Giuseppe Giudice
Comments: Latex2e, 19 pages, 3 tables, 10 figures, 18 references. Authorship changed; new figures added for a direct comparison with the observable quantities. Accepted for publication in New Astronomy
Subj-class: General Relativity and Quantum Cosmology; Space Physics
In this paper we investigate the effects that an anomalous acceleration as that experienced by the Pioneer spacecraft after they passed the 20 AU threshold would induce on the orbital motions of the Solar System planets placed at heliocentric distances of 20 AU or larger as Uranus, Neptune and Pluto. It turns out that such an acceleration, with a magnitude of 8.74\times 10^-10 m s^-2, would affect their orbits with secular and short-period signals large enough to be detected according to the latest published results by E.V. Pitjeva, even by considering errors up to 30 times larger than those released. The absence of such anomalous signatures in the latest data rules out the possibility that in the region 20-40 AU of the Solar System an anomalous force field inducing a constant and radial acceleration with those characteristics affects the motion of the major planets.
http://arxiv.org/abs/gr-qc/0601055
Posted by: ljk4-1 Apr 17 2006, 05:43 PM
Paper (*cross-listing*): gr-qc/0604047
Date: Mon, 10 Apr 2006 13:33:42 GMT (601kb)
Title: Does a Teleconnection between Quantum States account for Missing Mass,
Galaxy Ageing, Lensing Anomalies, Supernova Redshift, MOND, and Pioneer
Blueshift?
Authors: Charles Francis
Comments: 20 pages, 12 figs. Submitted to Proc Roy Soc A
\\
Empirical implications of a teleparallel displacement of momentum between
initial and final quantum states, using conformally flat quantum coordinates
are investigated. An exact formulation is possible in an FRW cosmology in which
cosmological redshift is given by 1+z=a_0^2/a^2(t). This is consistent with
current observation for a universe expanding at half the rate and twice as old
as indicated by a linear law, and, in consequence, requiring a quarter of the
critical density for closure. After rescaling Omega so that Omega=1 is critical
density in the teleconnection model, it is found that for given cosmological
parameters, Omega, Omega_k and Omega_Lambda, luminosity distance is a factor
sqrt(1+z) greater than in the corresponding standard model. Best fits to data
from the SuperNova Legacy Survey for a flat space Lambda cosmology is
Omega=1.07 and for a Lambda=0 cosmology, Omega=1.15. It will require many
observations of supernovae at z>1 to eliminate either the standard or
teleconnection magnitude-redshift relation. Quantum coordinates exhibit an
acceleration in time, resulting in the anomalous Pioneer blue-shift and in the
flattening of galaxies' rotation curves. These appear as optical effects and do
not affect classical motions. Milgrom's phenomenological law (MOND) is
precisely obeyed. A no CDM teleconnection model resolves inconsistencies
between galactic profiles found from lensing data, rotation curves and analytic
models of galaxy evolution.
\\ ( http://arXiv.org/abs/gr-qc/0604047 , 601kb)
Posted by: edstrick May 12 2006, 10:04 AM
In a talk on the Pioneer Anomaly last week at the ISDC (see a few other comments in my post on a Pioneer imaging thread), two things emerged regarding the value of the recovered but not analyzed tracking data.
1.) The anomaly on both Pioneers in the current data does not vary with distance from the sun or time starting at about Uranus' orbit (current data availability) Extending the data much further inward will help search for non-constant forces, particularly ones due to heating of the spacecraft or reflectd sunlight, etc.
2.) Current data says the apparent force is radially inward toward the "inner solar system". The recovered data will enable testing of whether the force is toward the sun, toward the earth, along the spacecraft's axis of rotation (usually but not always exactly toward the earth), or aligned with the spacecrafts velocity vector relative to the sun. In the current data, all these directions are approximately the same and cannot be sorted out.
This will enable testing for and exclusion of a very large number of possible forces acting on the spacecraft. For example, the force of the transmitted radio beam is small but not trivial. That force is always along the spin axis and normally approximately ponited at Earth. For another example, Pioneer 11 was in a low eccentricity orbit around the sun between Jupiter and Saturn examples, and a "drag-like" force would be in it's direction of travel, not radially inward.
Posted by: ljk4-1 Jun 2 2006, 03:56 PM
Astrophysics, abstract
astro-ph/0504634
From: Andreas Rathke [view email]
Date (v1): Thu, 28 Apr 2005 15:19:02 GMT (163kb)
Date (revised v2): Thu, 1 Jun 2006 08:46:23 GMT (125kb)
Options for a nondedicated mission to test the Pioneer anomaly
Authors: Dario Izzo, Andreas Rathke
Comments: 29 pages, uses AIAA style files. Improved presentation, shortened, some technicalities from v1 omitted, updated references, to appear in Journal of Spacecraft and Rockets
The Doppler-tracking data of the Pioneer 10 and 11 spacecraft show an unmodelled constant acceleration in the direction of the inner Solar System. Serious efforts have been undertaken to find a conventional explanation for this effect, all without success at the time of writing. Hence the effect, commonly dubbed the Pioneer anomaly, is attracting considerable attention. Unfortunately, no other space mission has reached the long-term navigation accuracy to yield an independent test of the effect. To fill this gap we discuss strategies for an experimental verification of the anomaly via an upcoming space mission. Emphasis is put on two plausible scenarios: nondedicated concepts employing either a planetary exploration mission to the outer Solar System or a piggybacked micro-spacecraft to be launched from a mother spacecraft travelling to Saturn or Jupiter. The study analyses the impact of a Pioneer anomaly test on the system and trajectory design for these two paradigms. It is found that both paradigms are capable of verifying the Pioneer anomaly and determine its magnitude at 10% level. Moreover the concepts can discriminate between the most plausible classes of models of the anomaly, a central force, a blueshift of the radio signal and a drag-like force. The necessary adaptions of the system and mission design do not impair the planetary exploration goals of the missions.
http://arxiv.org/abs/astro-ph/0504634
Posted by: remcook Jun 2 2006, 06:22 PM
If you've got new scientist...there's an article about the pioneer anomaly:
http://www.newscientist.com/article/mg19025541.800.html
I haven't actually read it, but maybe someone can tell us what it's about
Posted by: Bob Shaw Jun 2 2006, 08:34 PM
QUOTE (remcook @ Jun 2 2006, 07:22 PM)
If you've got new scientist...there's an article about the pioneer anomaly:
http://www.newscientist.com/article/mg19025541.800.html
I haven't actually read it, but maybe someone can tell us what it's about
There's a plan to re-examine all the tracking data which still exists, and to tie down the specific trajectory deviations which should nail the problem - it turns out that the competing explanations all result in unique vectors being imposed upon the trajectory so there may yet be a clear answer. Oh, and the tracking data being used this time is for a much longer time period than previous analyses used.
Bob Shaw
Posted by: Richard Trigaux Jun 3 2006, 02:02 PM
QUOTE (Bob Shaw @ Jun 2 2006, 08:34 PM)
...it turns out that the competing explanations all result in unique vectors being imposed upon the trajectory so there may yet be a clear answer...
Bob Shaw
That depend on. My prefered non-standard explanation would be that a small amount of dark matter would be linked to the solar system, creating a gravitationnal field which would peak at the distance of Jupiter or Saturn, decrease in 1/r2 beyond, and be null around Earth, because we would be inside this mass. If dark matter is formed of material weakly interacting particules, they still obey to gravitation, and thus they must be in orbit around the galaxy, at speeds in the 200/300km/s range. So it is expectable that some were caugh by the solar system and may orbit around it.
This said, I think we can seriously consider such kind of extraordinary hypothesis only after correct examination of all the existing data, and eliminating all the causes linked to the probe, solar wind, etc. Especially each hypothesis will have its own recognizable profile.
Posted by: dvandorn Jun 3 2006, 03:11 PM
Dark matter. It's so deliciously undefined that it can be used as a chimera, explaining away any mass or gravity anomalies without requiring us to put forth any kind of realistic or organized description of its behavior or organization.
What we observe of the visible universe shows that mass tends to clump. Yes, some percentage of the mass of the Universe is present in a non-clumped cloud of gas and dust that extends between the galaxies and is wrapped into and around galaxies. But the vast majority of the mass we can see and measure is all bound up in gravitationally significant clumps -- from small rocky bodies all the way up to supermassive black holes.
The only thing the theoreticians can tell us about dark matter is that it cannot be seen and does not interact with normal matter and energy -- except gravitationally. Regular matter and dark matter must interact gravitationally, or else the reason for proposing its existence in the first place simply goes away in a puff of logic.
Now, the Pioneer anomaly is, as I understand it, a very slight anomalous acceleration twoards the inner solar system. Which would indicate that there is some unmodeled mass in the inner system that isn't accounted for in our current understanding of the mass of the Sun and inner planets.
If dark matter is responsible for this unmodeled acceleration, should we be thinking in terms of a "clump" of dark matter somewhere in the inner system? Since it begs incredulity to believe that dark matter simply exists as a smooth soup of undetectable matter, do we assume that there is some "extra" mass somewhere in the inner system that can account for this?
If so, where does this extra mass show up in the motions of the planets?
It doesn't.
This leads me to believe that either the Pioneer anomaly is the result of a defect in measurement of the probe's trajectory, or a defect in our model of gravitation. I don't think it makes sense to postulate mass that only affects *some* other masses in the solar system, but not others.
-the other Doug
Posted by: The Messenger Jun 3 2006, 08:57 PM
QUOTE (Bob Shaw @ Jun 2 2006, 02:34 PM)
There's a plan to re-examine all the tracking data which still exists, and to tie down the specific trajectory deviations which should nail the problem - it turns out that the competing explanations all result in unique vectors being imposed upon the trajectory so there may yet be a clear answer. Oh, and the tracking data being used this time is for a much longer time period than previous analyses used.
Bob Shaw
Anderson & company had trouble mapping solar wind acceleration coefficients for both Gemini and Galileo-They ended up adding an additional term that varied by ~1/r at a magnitude much greater than the Pioneer anomaly. Since this factor held an exactly solar vector, it is impossible to differentiate the 'unexpected force' from an unexpected attenuation in the solar wind. (Which could be as simple as deionization over time and distance.)
If the bulk of the Pioneer data leads to a similar conclusion, the next step may be something to give us a better feel for the solar wind...Something like the Planetary Society's solar sail
Posted by: Richard Trigaux Jun 4 2006, 07:51 AM
dvandorn, I quoted this explanation based on dark matter only to say that all the competing hypothesis would not give a constant acceleration. In the instance, dark matter would form a symmetrical fuzzy cloud all around the Sun (like it does around galaxies). If so, we could detect it as an acceleration toward the sun, peaking somewhere around Jupiter and Saturn, and decreasing inside or beyond. So if we found such a behaviour, we could point at such an explanation.
But I agree with you that such explanations are not very likely, and that only the complete examination of the full data set and eliminating all the standard hypothesis (like de-ionisation of the solar wind, as says The Messenger) will allow is to take non-standard hypothesis as working hypothesis.
What I am afraid is that, even if the problem is fixed in a standard way, there will be still tens of years of speculation and nutter litterature about it...
Posted by: ljk4-1 Jun 6 2006, 03:41 AM
Centauri Dreams' latest take on the Pioneer Anomaly, including
descriptions of what was almost lost in terms of data on and from
Pioneer 10 and 11.
To quote:
New Scientist is running an interesting piece [subscription required for full access] on Slava Turyshev (JPL), who plans to investigate the so-called Pioneer Anomaly by re-flying the mission virtually. It’s a fascinating tale for various reasons, not the least of which is how close we came to losing much if not all of the precious Pioneer data.
For one thing, 400 reels of magnetic tapes housing information about the trajectories of the two spacecraft had to be saved from years of neglect and transferred to DVD.
Full article here:
http://www.centauri-dreams.org/?p=688
Posted by: Richard Trigaux Jun 6 2006, 05:39 AM
That is great new at last that the data was saved, and that it is now available for correct study.
To summarize, some of the main hypothesis, from the likeliest from the unlikeliest.
-interaction between the ship and the solar wind and radiation was not modeled corectly, or was made wrong by some unexpected thing (for instance paint changing of color with UV)
-solar wind don't behave as expected (for instance de-ionization)
-there is an unknown planet of a significant mass (things like brown star, white dwarf, black holes... seem too large, unless they are very far)
-there is an invisible cloud of matter in close vicinity of our solar system (this was also debated about the low frequency noise in the cosmic background)
-there is an unconventionnal mass around there, such as a bit of dark matter
-there are unknown novel physical effects
-1/R2 gravitation law would be no longer valid at larger distance (MOND hypothesis) which would also explain the behaviour of galaxies and galaxy clusters without dark matter.
With my opinion those hypothesis should be examined into this order, and we should pass from a likelier hypothesis to an unlikelier one only if th first is proven false.
Posted by: Bob Shaw Jun 6 2006, 02:12 PM
According to the NS article, the data tapes were just about to go in a skip when Our Hero arrived to save them! Great skin of the teeth stuff!
Bob Shaw
Posted by: ljk4-1 Jun 6 2006, 02:26 PM
Maybe something attached themselves to the Pioneers....
Posted by: Richard Trigaux Jun 6 2006, 03:39 PM
QUOTE (ljk4-1 @ Jun 6 2006, 02:26 PM)
Maybe something attached themselves to the Pioneers....
space leeches?
Posted by: ljk4-1 Jun 6 2006, 06:31 PM
30 Years of Pioneer Spacecraft Data Rescued:
The Planetary Society Enables Study of the Mysterious Pioneer Anomaly
Pasadena, CA, - There's a mystery at the edge of our solar system. Two
spacecraft, Pioneers 10 and 11, which were launched to Jupiter and
Saturn more than 30 years ago, are hurtling towards the edge of our
solar system -- but at a slower than expected rate. Called the "Pioneer
Anomaly," http://planetary.org/programs/projects/pioneer_anomaly/ the
effect of this slowing is small, but measurable, and so far unexplained.
Full article here:
http://planetary.org/about/press/releases/2006/0605_30_Years_of_Pioneer_Spacecraft_Data.html
Posted by: The Messenger Jun 7 2006, 01:18 AM
QUOTE (Richard Trigaux @ Jun 5 2006, 11:39 PM)
That is great new at last that the data was saved, and that it is now available for correct study.
To summarize, some of the main hypothesis, from the likeliest from the unlikeliest.
1-interaction between the ship and the solar wind and radiation was not modeled correctly, ...)
2-solar wind don't behave as expected (for instance de-ionization)
3-there is an unknown planet of a significant mass ..
4-there is an invisible cloud of matter in close vicinity of our solar system...
5-there is an unconventionnal mass around there, such as a bit of dark matter
6-there are unknown novel physical effects
7-1/R2 gravitation law would be no longer valid at larger distance (MOND hypothesis) ...
we should pass from a likelier hypothesis to an unlikelier one only if th first is proven false.
The linearity of what we have observed rules-out items one through five, unless both probes experienced virtually identical, linear responses to what should be non-linear functions (possible, but peculiar). It is disappointing to me, that after all the careful analysis Anderson, Nieto and Turyshev have given to us, a mission dedicated to nailing this down is not a major priority. There are a lot of dots that need to be connected.
Posted by: Richard Trigaux Jun 7 2006, 05:34 AM
QUOTE (The Messenger @ Jun 7 2006, 01:18 AM)
The linearity of what we have observed rules-out items one through five, unless both probes experienced virtually identical, linear responses to what should be non-linear functions (possible, but peculiar). It is disappointing to me, that after all the careful analysis Anderson, Nieto and Turyshev have given to us, a mission dedicated to nailing this down is not a major priority. There are a lot of dots that need to be connected.
Linearity? I have heard several versions, a force toward the Sun for Pioneers, backward for others... We really need to study the data, and obtain real curves, not just some dots.
Posted by: The Messenger Jun 7 2006, 06:20 PM
QUOTE (Richard Trigaux @ Jun 6 2006, 11:34 PM)
Linearity? I have heard several versions, a force toward the Sun for Pioneers, backward for others... We really need to study the data, and obtain real curves, not just some dots.
The residual acceleration in the plots in the Anderson & co definitive paper are quite linear at distances competing effects from solar pressure can be seperated from the anomaly >12AU (~-8x10^-10m/s^2). It is clear from their work that they think this effect extends into the inner solar system (where it may or may not appear to be linear), but they are only able to state that the anomally is not a function of raw solar pressure after the residual acceleration becomes negative.
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf p19-20
There is at least one more unprobability you should add to the list: A very slight increase in the speed of the light used to measure the acceleration. In one of the papers ljk4-1 posted above, they demonstrated that the pioneer anomalies can be modeled as a lensing effect; which effectively means the speed of light increases with increasing distance from the sun. GR already allows this (expressed as space 'de' contraction), but the magnitude would have to be many times greater than predicted by GR - this may or may not fall into the 'unknown-novel' category.
Posted by: Richard Trigaux Jun 7 2006, 08:27 PM
Speed of the light??
What is the speed of the light in an ionized medium like the solar wind? Certainly a bit slower than c. Was this effect accounted for? And if so, was the model accounting with eventual de-ionization of the solar wind? or other anisotropy, like magnetic field keeping part of the wind into the ecliptic plane?
Posted by: ljk4-1 Jun 9 2006, 08:06 PM
Astrophysics, abstract
astro-ph/0606197
From: Mauro Sereno [view email]
Date: Thu, 8 Jun 2006 15:28:39 GMT (49kb)
Dark matter vs. modifications of the gravitational inverse-square law. Results from planetary motion in the solar system
Authors: M. Sereno (Univ. Zuerich), Ph. Jetzer (Univ. Zuerich)
Comments: 7 pages, 4 figures, accepted for publication in MNRAS
Dark matter or modifications of the Newtonian inverse-square law in the solar-system are studied with accurate planetary astrometric data. From extra-perihelion precession and possible changes in the third Kepler's law, we get an upper limit on the local dark matter density, rho_{DM} < 3*10^{-16} kg/m^3 at the 2-sigma confidence level. Variations in the 1/r^2 behavior are considered in the form of either a possible Yukawa-like interaction or a modification of gravity of MOND type. Up to scales of 10^{11} m, scale-dependent deviations in the gravitational acceleration are really small. We examined the MOND interpolating function mu in the regime of strong gravity. Gradually varying mu suggested by fits of rotation curves are excluded, whereas the standard form mu(x)= x/(1+x^2)^{1/2} is still compatible with data. In combination with constraints from galactic rotation curves and theoretical considerations on the external field effect, the absence of any significant deviation from inverse square attraction in the solar system makes the range of acceptable interpolating functions significantly narrow. Future radio ranging observations of outer planets with an accuracy of few tenths of a meter could either give positive evidence of dark matter or disprove modifications of gravity.
http://arxiv.org/abs/astro-ph/0606197
Posted by: Richard Trigaux Jun 10 2006, 07:49 AM
Very interesting work.
Now just remains to compare the pioneer effect to the above results. If the Pioneer effect is larger, its origin must be searched into trite explanations (solar wind interaction and the like). The only interesting explanation would be about an unexpected behaviour of the solar wind.
Posted by: ljk4-1 Aug 15 2006, 09:45 PM
I wonder if the recently announced one quadrillion members of the outer
Sol system play any role in the Pioneer Anomaly?
Posted by: ljk4-1 Sep 2 2006, 08:11 PM
Test of the Pioneer anomaly with the Voyager 2 radio-ranging distance measurements to Uranus and Neptune
http://arxiv.org/abs/gr-qc/0608127
Posted by: NMRguy Mar 27 2007, 09:34 AM
After a long hiatus, the Pioneer Anomaly finally resurfaces in the news circuit with an article from Space.com.
"Researchers want to determine whether heat from Pioneer probes’ electronics or two nuclear power sources—known as radioisotope thermal generators (RTGs)—could be emitting infrared photons that then smack into the spacecraft’s dish-like main antenna, causing a recoil effect that Turyshev likened to sunlight striking a solar sail.
Analysis and modeling of how the Pioneer 10 spacecraft emits heat from various sources, including its RTG, found that they account for between 55 percent and 75 percent of Pioneer Anomaly, said Gary Kinsella, a group supervisor for spacecraft thermal engineering and flight operations at JPL. "
http://space.com/scienceastronomy/070327_scitues_pioneeranom.html
Posted by: Littlebit Mar 27 2007, 03:26 PM
QUOTE (NMRguy @ Mar 27 2007, 03:34 AM)
"Researchers want to determine whether heat from Pioneer probes’ electronics or two nuclear power sources—known as radioisotope thermal generators (RTGs)—could be emitting infrared photons that then smack into the spacecraft’s dish-like main antenna, causing a recoil effect that Turyshev likened to sunlight striking a solar sail.
Analysis and modeling of how the Pioneer 10 spacecraft emits heat from various sources, including its RTG, found that they account for between 55 percent and 75 percent of Pioneer Anomaly, said Gary Kinsella, a group supervisor for spacecraft thermal engineering and flight operations at JPL. "
I can see a problem right off the top with this scenario: The thermal output from the RTGs diminished considerably during the ten-plus years that the probes were monitored - but the measured acceleration anomaly during the same period was constant. (In order for the two effects to be related, you would have to explain why the depleting RTGs would result in constant acceleration.)
Posted by: tedstryk Mar 27 2007, 03:37 PM
Most of the power loss is due to the degradation of the electronics - the actual decline in the output of the plutonium is much less pronounced.
Posted by: NMRguy Mar 28 2007, 09:57 PM
The problem with the most recent space.com article is that it really lacked details, and their “preliminary results” had huge error bars. I’m going to wait for more concrete conclusions to come out in publication.
In the mean time, a very nice account of the progress and data recovery just showed up at the Planetary Society. (Thanks, Emily!) It’s a very nice read on the challenges of handling and eventually analyzing data generated over very long time periods. When the “experiment” started, computer technology was still very young.
Slava Turyshev gives a few details on the thermal modeling, but stops short of the claims in the space.com article.
"Our thermal modeling of the Pioneer vehicles is progressing very well. We finished the development of the geometric mathematical models of the spacecraft that include geometry and properties of most of the important spacecraft components and surfaces. We are now working on the thermo-dynamical model of the vehicles. At this stage, we have a very good understanding of heat re-distribution within the craft and soon will be ready to compute the heat flow to the outside of the craft. Soon, we will be able to tell whether or not heat contributes to the formation of the anomaly."
http://planetary.org/programs/projects/pioneer_anomaly/update_20070328.html
Posted by: elakdawalla Mar 28 2007, 10:00 PM
You're welcome, but Slava wrote it; all I did was post it. I'll be happy to forward your thanks on to him.
--Emily
Posted by: nprev Mar 29 2007, 04:12 AM
Not to drift into tin-hat-land at all, but I keep wondering if our imperfect understanding of the true value of the gravitational constant might be the ultimate culprit here. Experimental results for G are inevitably wildly different from one another even at the third digit past the decimal point, which implies uniquely large uncertainty for a physical constant (insert various curses for the fact that the Earth is not a uniform sphere of homogeneous composition here! ) Can't understand why the particularly large error bars for this constant might not encompass the domain of the anomaly.
Try G=6.671281904 exp -11. If it works, I'll explain why via private correspondence in order to ensure that UMSF does not stray outside forum guidelines during the discussion (a distasteful possibility given the crackpot aura around gravitation); if not, forget I said anything, and thanks for the reality check. That's a firm heuristic, period.
Posted by: Comga Apr 4 2007, 04:18 AM
QUOTE (tedstryk @ Mar 27 2007, 08:37 AM)
Most of the power loss is due to the degradation of the electronics - the actual decline in the output of the plutonium is much less pronounced.
The half-life of the Pu 238 is 87 years. Since 1977 their thermal output has dropped ~21%.
Some of the reduction in electrical power generation is also due to the changing temperature differential, which decreases the efficiency of the thermal energy. Perhaps this is what you meant by "degradation of the electronics". However, this does not play into the net thrust of the thermal radiation.
Posted by: Comga Apr 4 2007, 04:21 AM
QUOTE (nprev @ Mar 28 2007, 09:12 PM)
Not to drift into tin-hat-land at all, but I keep wondering if our imperfect understanding of the true value of the gravitational constant might be the ultimate culprit here.....
IIRC, while our knowledge of the value of G is imperfect, our knowledge of the gravitational constant of the sun is very precise. So our value for G could be in error on the low side, but then our measure of the mass of the Sun would be in error on the high side, or vice versa.
Posted by: edstrick Apr 4 2007, 07:42 AM
Radiation damage to the thermoelectric diodes causes a large fraction of the total power decline in RTG's. It's minor for a normal mission, but nukes your power margins (don't pardon the pun), on a decades long mission.
Posted by: lyford Jun 27 2007, 05:19 AM
http://space.newscientist.com/article/dn12070-exotic-cause-of-pioneer-anomaly-in-doubt.html
08:00 22 June 2007
NewScientist.com news service
David Shig
QUOTE
The 'Pioneer anomaly' – the mystifying observation that NASA's two Pioneer spacecraft have drifted far off their expected paths – cannot be explained by tinkering with the law of gravity, a new study concludes.
....
Now, Kjell Tangen, a physicist at the firm DNV in Hovik, Norway, says tweaking the law of gravity in a variety of ways cannot explain the anomaly – while also getting the orbits of the outer planets right. After modifying gravity in ways that would match the Pioneer anomaly, he inevitably got wrong answers for the motion of Uranus and Pluto.
Posted by: Mongo Jun 27 2007, 02:27 PM
The big difference between the Pioneer spacecraft and any solar planet is that the planet is in a bound orbit, while the Pioneers are in an unbound trajectory.
What if the 'Pioneer Anomaly' is dependant on radial velocity from the Sun, being zero if the object's radial velocity is zero, increasing in a linear fashion towards the Sun for objects moving outwards, and increasing in a linear fashion away from the Sun for objects moving inwards.
A planet in a bound orbit would by definition have equal amounts of inward and outward movement, so over the whole orbit the 'Pioneer Effect' would be canceled out. The amount of displacement over the orbit would be impossible to detect, due to its small magnitude (because of the small radial velocities), working over short timespans (half an orbital period).
The Pioneers, by contrast, have much higher outward radial velocities, causing the anomalous effect to be larger, unbound trajectories, allowing the magnitude of the effect to build up over time instead of being canceled out, and were tracked by radio, allowing for much smaller effects to be noticed than is the case with the planets, whose positions must be optically observed. If the planets deviate by a few km at most, then return to the calculated positions every orbit, the deviation would go un-noticed. (Radar may change this in the future, at least for the nearby planets -- but are they looking for the effect?)
edit -- In addition, the 'Pioneer effect' would simply slightly decrease the eccentricity of a planetary orbit, pushing the perihelion out a few km, and the aphelion in a few km. It might have been already detected, but misinterpreted as a slightly lower 'true' eccentricity for that planet than the actual value.
Bill
Posted by: ngunn Jun 27 2007, 03:13 PM
QUOTE (Mongo @ Jun 27 2007, 03:27 PM)
A planet in a bound orbit would by definition have equal amounts of inward and outward movement, so over the whole orbit the 'Pioneer Effect' would be canceled out.
Bill
If this were true a planet would gain less potential energy on the outward path than it lost on the inward one, making a net energy gain on every orbit. Over a long enough period of time I think this would produce fairly spectacular results.
Posted by: Littlebit Jun 27 2007, 03:20 PM
Interesting comment within the article:
http://space.newscientist.com/article/dn12070-exotic-cause-of-pioneer-anomaly-in-doubt.html
QUOTE
Myles Standish, who calculates solar system motions at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, says most scientists suspect the asymmetrical radiation of heat from the spacecraft is to blame.
But he also acknowledges that the orbits of Uranus, Neptune and Pluto have not been measured as precisely as those of the inner planets, suggesting the new study by Tangen cannot rule out modified gravity as a cause. "The measurements are not able to support any definite conclusions," he told New Scientist.
Tangen did not consider the cases which would involve violation of the equivalence principle, so Tangen has only addressed a small subset of possible scenarios, establishing modest constraints.
If the anomaly is a function of the radial velocity relative to the sun as Mongo supposed; if I remember right, Pioneer 11's last gravitational assist swung it initially on a vector that passed closer to sun than the Saturn orbit. The extended data set retrieved by the Planetary Society includes this period, so any radial dependance may be apparent in this extended data set.
Posted by: Mongo Jun 27 2007, 04:35 PM
QUOTE (ngunn @ Jun 27 2007, 03:13 PM)
If this were true a planet would gain less potential energy on the outward path than it lost on the inward one, making a net energy gain on every orbit. Over a long enough period of time I think this would produce fairly spectacular results.
I am not sure I follow here. A planet on the 'outward' half of its orbit would be pulled slightly inward, as if the Sun's gravitational pull were slightly stronger, and on the 'inward' half of its orbit would be pushed slightly outward, as if the Sun's gravitational pull were slightly weaker. The sum of the inward and outward phases would be the same as if the Sun's gravitational pull were constant at its true value, provided that the effect is linear with radial velocity -- as can be proven using elementary geometrical arguments.
There is one possible observable effect: because of the slight difference in the Sun's effective gravitational pull between bodies moving toward or away from the Sun, the 'outward' phase of the planet's orbit would last slightly less long than the 'inward' phase (in order for the energy transfer to balance between the two phases, and also because the planet would 'decelerate' moving outwards more quickly than it would 'accelerate' moving inwards). This difference would be very small -- perhaps a few minutes? -- but might possibly result in a detectable deviation from a perfectly elliptical orbit. Although the deviation would be extremely small.
Bill
Posted by: ngunn Jun 27 2007, 04:41 PM
Energy is the integral of force over distance, so if the force is greater going one way than the other then energy is not conserved around a closed orbit.
Posted by: Mongo Jun 27 2007, 05:02 PM
I am not sure that this applies here, though. Force is defined as mass times acceleration, and the Pioneer effect could be viewed as if the inertial mass of the planet were slightly lower on the outbound phase of its orbit than on the inbound phase. (Hence the increased apparent gravitational pull of the Sun -- the acceleration would be determined by the Sun's gravitational acceleration at that distance times the ratio between the planet's standard mass and its inertial mass. If the inertial mass were half the standard mass, the planet would decelerate at twice the 'expected' rate) The slightly higher deceleration of the planet, times the slightly smaller inertial mass, would result in the same force due to gravity being applied to the planet as there would be under standard physics.
Bill
Posted by: ngunn Jun 27 2007, 05:15 PM
Are you saying it's inertia would be different in the radial direction from what it would be at 90 degrees to that direction? I'm not at all happy with that idea. Mass is a scalar property - or are you saying not in this case? I'm off home now but will continue to mull it over . .
Posted by: Mongo Jun 27 2007, 06:49 PM
Well... (thinking about it) ...I would assume that the gravitational force exerted on the orbiting body always remains the same as it would be under 'standard' physics, for the reason that you had mentioned. But in addition to the the 'standard' effect that varies with radial distance, approaching zero as radial distance R approaches infinity, and inversely proportional to the square of the radial distance:
1) f1 = G1*m1*m2*R^-2
Where f1 is the 'actual' gravitational force exerted on the body, and G1 is Newton's gravitational constant. A second-order effect of that force on the object's trajectory would vary with radial velocity (distance over time), reaching zero as radial velocity reaches zero, and linearly proportional to (the negative of) the radial velocity:
2) f2 = -Ga*m1*m2*v
Where f2 is the pseudo-force exerted on the body, v is the radial velocity and Ga is a second gravitational constant, possibly equal to G1. f2 would be much smaller than f1 at non-relativistic velocities, reaching zero as v reaches zero, but I would not be surprised if it approached f1 as v approaches c, so that Ga equals G1. Combining the two:
3) f1+f2 = (G1*m1*m2*R^-2) - (Ga*m1*m2*v)
The 'Pioneer effect' can be viewed as a modification of the well-known Newtonian force f1:
4) f2 = f1*R^2*v*G2 where G2 = Ga/G1
Resulting in:
5) f1+f2 = (G1*m1*m2*R^-2)*(1 - R^2*v)
if G1 = Ga, as I think it could be.
So, again assuming that Ga = G1, the change in the second-order 'force' must be proportional to v, with the inertial mass equal to the first object's rest mass times (1-v) in natural units (c = 1). This is of course the opposite effect as that described in special relativity, in that with special relativity, the inertial mass equals the rest mass times the square root of (one over (1-v))
Bill
Posted by: ngunn Jun 27 2007, 09:56 PM
QUOTE (Mongo @ Jun 27 2007, 07:49 PM)
This is of course the opposite effect as that described in special relativity
Bill
Have you worked out what that would do to the perihelion of Mercury?
Posted by: Mongo Jun 27 2007, 10:25 PM
I was looking at a paper discussing modified-inerta MOND theories, and came across the following (MI = Modified Inertia, MG = Modified Gravity):
http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0510/0510117v1.pdf
MOND as Modified Inertia
QUOTE
Closer to home, the Pioneer anomaly, if verified as a new-physics effect (Anderson et al. 2002), might provide a decisive test. It can be naturally explained in the context of MOND as MI but is difficult to explain in the context of a MG theory (Milgrom 2002): The Pioneer anomaly has no match in planetary motions for which a constant, unmodelled acceleration of the magnitude shown by the spacecraft is ruled out by a large margin. The planets probe heliocentric radii smaller than where the Pioneer anomaly has been found. So a MG theory may still have a little leeway by having the anomaly set in rather abruptly with distance just at the interim heliocentric radii (e.g., Sanders 2005). A MI explanation will build on the fact that the orbits of the spacecraft differ greatly from those of the planets: the former are close to linear and unbound, the latter quasi circular and bound. It is intriguing in this connection that the analysis for Pioneer 11 (Anderson et al. 2002) shows an onset of the anomaly just around the time where the spacecraft was kicked from a bound, nearly elliptical orbit to the unbound, almost linear orbit on which it is now (the corresponding event for Pioneer 10 is not covered).
The onset still wants verification, but if real, it would be a signature of MI.
If the Anderson analysis of the anomaly is correct, then the 'Pioneer effect' will never be detected in the orbits of the planets. A radio transponder (or possibly a laser reflector) placed on an unbound Solar-escape trajectory would be needed to study it.
Bill
Posted by: frankm Aug 9 2007, 03:39 AM
The Deen report provides a different way to present the telemetry blueshift.
Although the Pioneer 10/11 anomaly is presented as a "sunward acceleration", the actual data is the continuing blueshift of the telemetry signal. A researcher prepared a report that proposed a mechanism for the blueshift, it being caused by a changing "index of refraction" in what amounts to a segmented cosmic lens about the sun.
http://www.vip.ocsnet.net/~ancient/Deen-2007-Pioneer-10-Anomaly.doc
It should be noted that the author inverted the algorithm normally used to calculate the index of refraction, n, see Para. 4 of the report. He held v constant (inside 20 AU) and allowed c to change as the spacecraft went outbound, thus resulting in an increasing value for n. The increasing n is directly proportional to the increasing blueshift with distance.
Para. 1 of the report states the effect quite directly, "A photon emitted by a spacecraft outside the entire onion would experience successive speed reductions as it crossed successive shell boundaries moving inwards towards the Sun."
I hold a slightly different view than Deen, as I doubt the volume surrounding the Sun is layered, it has a constantly changing index of refraction, starting at the Sun's surface and extending outward to the limit of the heliosphere (or beyond). It is easier to visually present the constantly changing density as a series of layers, otherwise the density at a given point in space will be a function of the inverse square of the distance.
The detected blueshifted telemetry frequency is a reflection of the average value of the velocity of the telemetry signal as received at earth from the spacecraft at any given point in time.
We know the index of refraction for EM waves has a value of 1 as measured in a vacuum on the earth's surface. (diffraction index)^2 = (relative permittivity)
Posted by: Littlebit Aug 9 2007, 02:36 PM
An increasing blueshift, due to a change in the index of refraction implies that the speed of light is increasing with increasing distance from the sun. We should expect this to a very small degree, because the solar wind is thinning (the absolute vacuum of space is becoming more absolute). I don't recall that the calculations used by Anderson & Co. including any terms for the decreasing density of the helosphere.
There is a problem with this interpretation: The rate of blueshifting should decrease with increasing distance; but the anomally, on the scale that it has been detected, is quite linear. Still thinking out loud, this does not rule out a refractive solution if the density of the solar wind is roughly constant in the same region. Its too bad we do not have a pioneer-like probe well beyond the helopause. It would be easy to rule out / rule in such a solution simply by looking at the redshift of the sun.
Posted by: frankm Aug 9 2007, 04:00 PM
The rate of blueshifting is decreasing with distance. Each segment, Figure 4 or Figure 5, represents the same acceleration magnitude but the time required to achieve the same magnitude, and same blueshift, of the previous period is increasing. Under Figure 4 of the article, Deen states,
QUOTE
Each of the slanting curves corresponds to the falling off by the inverse square of the distance.
I haven't found any mention in any of the Anderson&Co reports that the density of "something" is changing outbound from the sun.
I thought the Deen report was an interesting way to present the acceleration (blueshift) data. It makes it easier to visualize the persistence of the shift.
Posted by: frankm Aug 12 2007, 04:35 PM
In order to see the progression of the spherical shells illustrated in Deen's report, I replicated his nine pair of data points in a spreadsheet and extended the shells inward and outward. Deen's spherical shells follow the standard formula for such volumes.
What I really need is a spreadsheet algorithm that uses the primary anomaly variable, the value of the blueshift. I would like to see is how close the blueshift converges to zero at the Earth 1 AU distance.
Is there a report that gives the actual blueshift value at 20 AU?
Posted by: frankm Aug 14 2007, 10:54 PM
I found a neat site that allows one to put in a set of values and it returns the regression results.
http://people.hofstra.edu/stefan_waner/RealWorld/newgraph/regressionframes.html
My first set used R in and the refraction index and the second set R out and the refraction index. I didn't get a good fit with any regression process for R in, but had a near perfect fit with R out.
The best fit for the outer R gave an r = 1 the equation being y = ax^b with y =.000124956x^2
I suspect the way Deen extracted his data influenced the R in vs R out data sets, the actual refraction index being tied to the R out value.
This indicates that whatever is causing electromagnetic waves to change their velocity has a near perfect fit to the square of the distance.
Posted by: frankm Aug 20 2007, 03:33 PM
There were several structural problems with the Deen report, three equations did not display and the references were missing. The author has made his report available in pdf form and it includes all of the material.
http://www.glendeen.com/npa2007/Deen_2007_Pioneer_10_Anomaly.pdf
The primary reference [1] is available at arxiv.org and it is the 2005 revision. It is a 1.5 mb file.
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064v5.pdf
Posted by: tfisher Nov 22 2007, 03:04 PM
I just noticed the team working on data recovery put out a new update:
http://arxiv.org/abs/0710.2656.
They still aren't quite to the point of having a calibrated unified dataset -- by the end of the year, they say.
It does sound like their heat modeling project is going pretty well. I'm really hopeful that they will be able
to conclusively answer whether or not thermal forces can explain the anomaly.
Posted by: Harder Jan 29 2008, 08:45 PM
Catching up on reading ESO Messenger reports I came across an article in the June 07 edition (#128) in which Newton's law was tested in the low acceleration regime (outer regions-) of globular clusters. The rather astounding conclusion was that globular clusters behave like galaxies in that the velocity pattern in these outer regions flattens off in exactly the same pattern as measured for galaxies.
For this behaviour around galaxies it is widely assumed that large quantities of dark matter (hidden in the galaxies) are responsible. But for globular clusters this explanation is apparently not valid at all. Ergo, it seems that one of the main reasons for "inventing" dark matter in large scale gravity puzzles is no longer valid and that alternatives such as MOND gain a lot of credibility. Especially since it is "unpalatable" as the authors decribe it to assume that dark matter also is a pervasive factor in globular clusters. If someone could explain that to me that would be highly appreciated, but I take the word of the authors until advised otherwise.
A modified Newton law would also go a long way in describing the Pioneer anomaly I believe. This thread will probably remain open for quite some time to come. (Pls support Doug with his new server project )
To top it all off, in the Febr08 number of Ciel et Espace there is an article describing a new competitor for MOND, called MOG for Modified Gravity theory. The Pioneer anomaly, which started as a fairly low-key issue, seems on the up again now that Newtons law is shaking, at least in the low acceleration regime. What will be next??
Instead of citing the names of the authors, apologies if I should have done so, here is the link to Messenger #128. Read for yourself!
http://www.eso.org/sci/publications/messenger/archive/no.128-jun07/messenger-no128.pdf
Posted by: Mongo Jan 30 2008, 02:04 AM
http://www.unmannedspaceflight.com/index.php?s=&showtopic=4197&view=findpost&p=95206
Posted by: stevesliva Mar 31 2011, 05:28 AM
New work on thermal modeling the affect of IR scattering off of the back of the HGA purports to explain the entirety of the anomaly:
http://www.technologyreview.com/blog/arxiv/26589/
Posted by: stevesliva Jul 22 2011, 05:39 AM
And NASA takes another look:
http://www.technologyreview.com/blog/arxiv/27012/
(Links to referenced papers in both this and the last article.)
Posted by: Mongo Jul 22 2011, 04:23 PM
From http://arxiv.org/pdf/1107.2886v1
"The main question is whether or not a statistically significant anomalous acceleration signal still remains in the residuals after the thermal recoil force has been properly accounted for. Results of this meticulous study will be published soon."
Unfortunately, the paper does not appear to give error bars.
Assuming that the error bars are small enough that the above diagram (especially the "Stochastic Acceleration" portion) is reasonably accurate, it looks to me like the acceleration curve flattens out to an asymptotic value of about 7 x 10^-10 ms^-2.
The most obvious cause, in my opinion, would be an exponential decaying acceleration with a half-life of about 3-4 years (declining due to radioactive decay in the RTG?) plus a steady acceleration of unknown origin of about 7 x 10^-10 ms^-2.
Of course I am no expert.
Posted by: nprev Jul 23 2011, 12:15 AM
QUOTE (Mongo @ Jul 22 2011, 08:23 AM)
Of course I am no expert.
Posted by: Littlebit Oct 5 2011, 03:27 PM
The name of the game has always been to grow the thermal differentiation to the point that the error bars overlap the known radioactive decay profile; providing a plausible solution.
Posted by: gndonald May 12 2012, 09:27 AM
QUOTE (Littlebit @ Oct 5 2011, 11:27 PM)
The name of the game has always been to grow the thermal differentiation to the point that the error bars overlap the known radioactive decay profile; providing a plausible solution.
Looks like the mystery has been solved...
http://www.planetary.org/blogs/bruce-betts/3459.html
I'd also heard that the ESA was considering a mission to probe the effect, but I've not been able to find out much about it.
Posted by: Paolo May 12 2012, 11:25 AM
QUOTE (gndonald @ May 12 2012, 11:27 AM)
I'd also heard that the ESA was considering a mission to probe the effect, but I've not been able to find out much about it.
see for example
http://arxiv.org/abs/gr-qc/0506139, http://arxiv.org/abs/1106.0132, http://arxiv.org/abs/1107.2316
Posted by: tasp May 12 2012, 12:11 PM
LOL, sounds like UMSFs crack Ice Hunters might get a new gig.
Let's go get 'em a big un !!
Posted by: TheAnt May 18 2012, 10:03 AM
Not much reason to send one entire new mission or studies IMO.
The case might be quite closed and filed after JPL have had another look at the matter.
The paper by Francisco, Bertolami and Páramos is found here:
http://arxiv.org/pdf/1103.5222v2
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