The Pioneer Anomaly Options

[remcook]

http://www.planetary.org/news/2005/pioneer_anomaly_faq.html

The planetary society may be checking it out...

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 The Pioneer data exists on a few hundred ancient 7- and 9-track magnetic tapes, which can only be read on "antique" outdated computers.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!

[Mongo]

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

[The Messenger]

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.

[ljk4-1]

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)

[ljk4-1]

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)

[The Messenger]

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:

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)

[Mongo]

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