Does the PA show that DM/DE is dynamically important in the outer solar system?

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Main Question or Discussion Point

Reynaud and Jaekel's paper published in the Phsics ArXiv today:
Long range gravity tests and the Pioneer anomaly
(Report-no: LPTENS 06/46)
(Laboratoire de Physique The'orique de l'Ecole Normale Supe'rieure)
Abstract.
Experimental tests of gravity performed in the solar system show a good agreement with general relativity. The latter is however challenged by the Pioneer anomaly which might be pointing at some modification of gravity law at ranges of the order of the size of the solar system. As this question could be related to the puzzles of “dark matter” or “dark energy”, it is important to test it with care
If we follow the line of thought presented in this paper, the confrontation of data with extended metric theories of gravitation is of particular interest, as the anomaly observed on the trajectories of the Pioneer 10 & 11 probes may well be a first hint of a modification of gravity law in the outer part of the solar system. This possibility would have such a large impact on fundamental physics, astrophysics and cosmology that it certainly deserves further investigations. The evaluations presented in Ref. [26] will allow one to address these questions in a well defined theoretical framework. It is only after a quantitative comparison, taking into account the details known to be important for data analysis [13], that it will be possible to know whether the post-Einsteinian phenomenological framework shows the capability of fitting the Pioneer observations.
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  • #2
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I was under the impression that dark matter and energy had already been ruled out as possible explanations of the Pioneer anomaly.

Given how little data we actually have on the matter, I doubt anyone is going to figure it out any time soon. Certainly not until we have more data to compare with.
 
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Parlyne said:
I was under the impression that dark matter and energy had already been ruled out as possible explanations of the Pioneer anomaly.
Obviously not.

I don't think you can rule anything out at this stage, certainly not 'DM' or 'DE' whatever they are....
Given how little data we actually have on the matter, I doubt anyone is going to figure it out any time soon. Certainly not until we have more data to compare with.
Actually there is a lot of data, both on the Pioneer spacecraft, which have been tracked for thirty years with a consistent result for the anomalous acceleration from both spacecraft. Also other spacecraft have shown certain similar anomalies but where the signal is less 'clean'.

As the paper in my OP puts it:
It is worth emphasizing that the Pioneer anomaly has been registered on the two deep space probes showing the best navigation accuracy. Other anomalous observations have been reported for Ulysses and Galileo probes, but they were not as reliable as for Pioneer probes [13]. For other probes like Voyager 1 & 2 and Cassini, the navigation accuracy was not sufficient. In other words, the Pioneer gravity test has been performed twice with identical probes on similar trajectories - but escape directions opposite in the solar system - and the same result. This is not an impressive statistics when we compare it to the large number of tests confirming GR. In particular, when the possibility of an artefact onboard the probe or in its environment is considered, this artefact could be the same on the two probes. However, no satisfactory explanation of this kind has been found to date, though intensive efforts have been devoted to this aim. The extensive analysis of Anderson et al [13], published after years of cross checks, has been confirmed by an independent analysis [59]. Such independent reanalyses of the data remain an important tool to confirm or infirm the existence of the anomaly and they now experience a revival thanks to recently recovered data covering the whole period of Pioneer 10 & 11 missions from their launch to the last data point [60, 61, 62, 63].
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Garth said:
Obviously not.

I don't think you can rule anything out at this stage, certainly not 'DM' or 'DE' whatever they are....
Actually there is a lot of data, both on the Pioneer spacecraft, which have been tracked for thirty years with a consistent result for the anomalous acceleration from both spacecraft. Also other spacecraft have shown certain similar anomalies but where the signal is less 'clean'.
To be more specific, my understanding was that for DM or DE to be that relevant on the scale of the PA, we should also see effects on other bodies in the solar system.

As the paper in my OP puts it:
Garth
He pretty much makes every point that I could want to. All we have are results from two identical probes. If the problem were with them, we have no way of identifying it. Simply put, there just isn't enough data to draw firm conclusions.
 
  • #5
SpaceTiger
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Garth said:
Reynaud and Jaekel's paper published in the Phsics ArXiv today:
[URL [Broken] gr-qc/0610160]Long range gravity tests and the Pioneer anomaly[/URL]
(Report-no: LPTENS 06/46)
(Laboratoire de Physique The'orique de l'Ecole Normale Supe'rieure)
The paper can be found here:

http://www.arxiv.org/abs/gr-qc/0610160" [Broken]

I don't see how the subject heading of your post relates to this paper. The author makes reference to the "dark matter" and "dark energy" problems, but is talking only about modified gravity solutions to these problems. Dark matter and dark energy themselves don't enter into the analysis.
 
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Edit: crossed post: Thank you ST, I have now corrected the broken link in the OP.

Nobody is drawing firm conclusions, that is why I phrased the thread title as a question.

My point is, that after the drawing of a firm conclusion in another thread, now locked, that DM is not dynamically important in the solar system, a report is now published by Reynaud and Jaekel in which they raise the possibility of a link between the mysterious nature of DM/DE and the mysterious nature of the PA.

I believe no firm conclusions can be drawn about either mystery but rather an open mind should be kept; the resolution of one mystery may also provide the solution to the other.

I asked the question in the OP title in order to keep minds open.

Do you not find the PA intriguing?

Garth
 
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  • #7
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Garth said:
My point is, that after the drawing of a firm conclusion in another thread, now locked, that DM is not dynamically important in the solar system, a report is now published by Reynaud and Jaekel in which they raise the possibility of a link between the mysterious nature of DM/DE and the mysterious nature of the PA.
I don't think they're saying that. They're saying that the Pioneer anomaly is indicative of a problem with GR...the same thing pretty much all Pioneer anomaly folks have been saying. If true, this might remove the need for DM or DE, but it says nothing about whether DM or DE would be the cause of the acceleration.


Do you not find the PA intriguing?
It is interesting and I have no problem with it being discussed, but I think we should avoid bringing it up in too many threads, particularly in ones in which it's not particularly relevant.
 
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SpaceTiger said:
I don't think they're saying that. They're saying that the Pioneer anomaly is indicative of a problem with GR...the same thing pretty much all Pioneer anomaly folks have been saying. If true, this might remove the need for DM or DE, but it says nothing about whether DM or DE would be the cause of the acceleration.
Agreed, in which case the answer to the title question would be the negative.
It (PA) is interesting and I have no problem with it being discussed, but I think we should avoid bringing it up in too many threads, particularly in ones in which it's not particularly relevant.
I agree, it is worth discussion. This thread was prompted by the publication of the Reynaud and Jaekel paper.

The problem as I see it being threefold,

1. If the gravitational field is being modified in some way this modification does not show up in the orbits of the outer planets, even though the PA manifested itself as soon as the spacecraft cleared Saturn and other noise 'quietened' down.

2. If DE is the cause then the acceleration might be expected outwards from the Sun, i.e. some form of 'anti-gravity' effect operating in the opposite direction to Newtonian gravity as DE is meant to.

3. DM could be the cause but only if inside, sunwards, of the Pioneers' orbits, in which case that too should show up in the Outer Planets' orbits. (Note that an effect was first looked for to test for a Planet X; the surprise was not only was a signal discovered but it was the same for both spacecraft on opposite sides of the Sun.)

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  • #9
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Note also:

1. The acceleration is aP = (8.74 ± 1.33) × 10−10 m/s2.

2. What is actually measured is a time acceleration of at = (2.92 ± 0.44) × 10−18 s/s2).

3. The effect has been constant and equal for both spacecraft from 10AU - 90AU. (Pioneer 10 - Feb 2003) (Other effects swamped it when they were closer than than 10AU from the Sun.)

4. That 'normal physics' from On-Board Systematics can so far explain a maximum of:

i Radio Beam Reaction Force a = (1.10 ± 0.10) × 10−10 m/s2. .
ii Anisotropic Heat Reflection a = (−0.55 ± 0.55) × 10−10 m/s2. .
iii Differential Change of the RTG’s Radiant Emissivity a = 0.85 × 10−10 m/s2. .
iv Constant Electrical Heat Radiation as the Source: not viable.
v Helium Expulsion from the RTGs a = (0.15 ± 0.16) × 10−10 m/s2. .
vi Propulsive Mass Expulsion a = ±0.56 × 10−10 m/s2.
(source The Study of the Pioneer Anomaly: New Data and Objectives for New Investigation Turyshev et al.)

This makes a maximum total of an = (2.1 ± 0.8) × 10−10 m/s2 that can be caused by normal physics leaving at least a minimum anomalous acceleration of ax = (6.6 ± 2.1) × 10−10 m/s2 to be explained.

5. Furthermore note the Hubble acceleration cH = 7.2 × 10−10 m/s2, which is consistent with this unexplained residual.

The PA may therefore be cosmological and not local in nature, which would also explain why it does not show up in the closed orbits of the Outer Planets.

Garth
 
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  • #10
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I just think of this as one of those things to keep in mind as new theories of gravity come along. I won't be convinced there's a problem until we have a more reliable measurement.
 
  • #11
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Garth, there is a very cute http://arxiv.org/abs/gr-qc/0602002" [Broken], published this year in Phys. Lett. B, that compares the supposed PA with Mercury's perihelion shift to demonstrate that the former is not due to DE.

After reading what peer reviewed papers are referenced on the wikipedia PA article, the scientific consensus seems very clear that the PA data is inconclusive (especially due to likely systematic errors), so we have no physical basis for discussion. Personally I'd love to see a better probe sent to investigate, but obviously someone needs to finance it. Otherwise, I understand outer planets are too slow to provide useful data, and if eccentric asteroids were easy to track precisely then I'm guessing someone would have done so about now.
 
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cesiumfrog said:
Garth, there is a very cute http://arxiv.org/abs/gr-qc/0602002" [Broken], published this year in Phys. Lett. B, that compares the supposed PA with Mercury's perihelion shift to demonstrate that the former is not due to DE.

After reading what peer reviewed papers are referenced on the wikipedia PA article, the scientific consensus seems very clear that the PA data is inconclusive (especially due to likely systematic errors), so we have no physical basis for discussion. Personally I'd love to see a better probe sent to investigate, but obviously someone needs to finance it. Otherwise, I understand outer planets are too slow to provide useful data, and if eccentric asteroids were easy to track precisely then I'm guessing someone would have done so about now.
Agreed, we need more information about the PA - but note the paper: "The Study of the Pioneer Anomaly: New Data and Objectives for New Investigation by Turyshev et al." was published in a peer reviewed journal: Journal-ref: Int.J.Mod.Phys. D15 (2006) 1-56.

I myself also do not believe that it is caused by DE, see my comment above, especially if DE is thought to be the cosmological constant as in your link paper. At present we have no firm idea about what DE actually is. However, the point I was making, and picked up from the OP paper, was that the two causes, one for the need for DE, and the other for the PA, could be related.

My main point is for us not to be too confident that we have modelled gravitation correctly, and minds should be kept open.

The question it leaves us is, "What then is the cause of the unexplained residual PA time drift?"

Garth
 
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  • #13
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What is the cause of the unexplained residual PA time drift?

Summing up:

1. The PA is measured as a residual blue doppler shift on signals returned back to Earth. The value of the frequency change is equal to:

ad = (2.92 ± 0.44) × 10−18 s/s2).

This can be interpreted as an acceleration (either towards the Sun or the Earth) equal to:

aP = (8.74 ± 1.33) × 10−10 m/s2.

2. After possible on-board systematics forces are taken into account there is still a real minimum residual acceleration of:

ax = (6.6 ± 2.1) × 10−10 m/s2 to be explained.

3. The anomalous acceleration is not dependent on range from the Sun. It appeared once the Pioneer spacecraft were gravity assisted by Saturn onto hyperbolic orbits. In any case before those encounters the effect would have been swamped by other effects, namely the solar radiation pressure and thruster gas leakage.

4. It does not show up in the orbital dynamics of the outer planets.
This alone indicates to me that it cannot be modelled by modification in the gravitational field of the Sun. See Iorio's eprint Can the Pioneer anomaly be of gravitational origin? - answer: negative. Therefore, like ST, I also conclude that the answer to the OP question is negative, DM/DE is not dynamically important in the Outer Solar System.

5. However, there is either another unknown reaction force acting on the spacecraft, but every conceivable possibility has already been tried unsuccessfully, or the effect is actually a clock drift between atomic clock time and ephemeris time.

6. I conclude therefore that the PA is caused partly by conventional physics i.e. a reaction force acceleration equal to a maximum value of:

ar = (2.1 ± 0.8) × 10−10 m/s2

and a clock drift or 'clock acceleration' of at least:

at = (2.2 ± 0.7) × 10−18 s-1.

I note that Hubble's constant in similar units (1/(Hubble Time) expressed in seconds) is equal to:

H = (2.4 ± 0.2) × 10−18 s-1 (h=0.73) and where I have given H ±10% error bars.

I find the consistency between at and H more than intriguing! A further conclusion is therefore that the PA is cosmological in origin and has been subsumed into the orbital dynamical model of the outer planets, which are on closed orbits. The effect only became observable when an accurate orbital determination was possible on spacecraft on open, hyperbolic, trajectories.

Viable gravitational theories that predict such a clock drift should be given due consideration.

Garth
 
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  • #14
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If cosmological effects could be seen on the solar system scale, we would also have to see that the galaxy was expanding along with the rest of the universe, which is manifestly not the case.
 
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Parlyne said:
If cosmological effects could be seen on the solar system scale, we would also have to see that the galaxy was expanding along with the rest of the universe, which is manifestly not the case.
While we actually do not know what the galaxy is doing as far as Hubble expansion is concerned, as Hubble velocities on our galaxy's scale are far smaller than the individual velocities of stars and spiral arms (Hubble expansion on galactic scales ~ 2 km/sec ~1% individual velocities), and it is generally thought the galaxy remains gravitationally bound w.r.t. the Hubble expansion, the effect I have concluded is a drift between atomic and ephemeris clocks, which would not manifest itself as such an expansion/contraction in either the galaxy or the orbits of the outer planets.

But, on the other hand Parlyne, what is your explanation of the PA?

Garth
 
  • #16
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As I said before, we really don't even have enough data to conclusively demonstrate that there really is a Pioneer Anomoly (or at least one that isn't the result of some sort of systematic effect related only to the Pioneer probes themselves).
 
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Parlyne said:
As I said before, we really don't even have enough data to conclusively demonstrate that there really is a Pioneer Anomoly (or at least one that isn't the result of some sort of systematic effect related only to the Pioneer probes themselves).
That is one point of view, however, others would disagree: Can conventional forces really explain the anomalous acceleration of Pioneer 10/11 ? Journal-ref: Int.J.Mod.Phys. D13 (2004) 865-870
We have provided a conventional and quantitative explanation to the small difference of magnitude of the anomalous acceleration observed between the Pioneers 10 and 11. As observed by Anderson et al. [7], we find that this is related to the difference of spin-rate history for both spacecraft. Now, these authors have shown that when the spin-rate change contribution is removed, one is left with an anomalous acceleration aP(0) of the same amount with a great accuracy during a very long time interval for both Pioneer 10/11 to explain. Since the Pioneers 10 and 11 are remote spacecraft moving in opposite directions from the Sun, this makes difficult to understand such a persistant constant anomalous acceleration in terms of conventional physics. Hence, the conventional explanation we suggest for the Pioneer 10/11 anomalous acceleration versus spin-rate change points out in favour of the possibility that something new of physical interest may be responsible of the main Pioneer anomaly at the expense of any possible internal cause.
It's "the possibility that something new of physical interest" that whets my appetite!

Garth
 
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  • #18
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I also like the possibility of new physics; but, first we have to be sure there's actually a phenomenon that needs explaining. So, the most important question is whether every possible source of systematic error (including in our prediction of where the probes should be) has already been eliminated.
 
  • #19
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Parlyne said:
I also like the possibility of new physics; but, first we have to be sure there's actually a phenomenon that needs explaining. So, the most important question is whether every possible source of systematic error (including in our prediction of where the probes should be) has already been eliminated.
Agreed! - Though I think international teams have already tried to do just that.

Garth
 
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