The Pioneer Anomaly Options

[remcook]

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

[Bob Shaw]

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

[Guest_Richard Trigaux_*]

...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.

[dvandorn]

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

[The Messenger]

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

[Guest_Richard Trigaux_*]

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...

[ljk4-1]

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

[Guest_Richard Trigaux_*]

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.

[Bob Shaw]

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

[ljk4-1]

Maybe something attached themselves to the Pioneers....

[Guest_Richard Trigaux_*]

Maybe something attached themselves to the Pioneers....

space leeches?

[ljk4-1]

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/...craft_Data.html

[The Messenger]

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.

[Guest_Richard Trigaux_*]

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.

[The Messenger]

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.