Physical Anomaly of the Pioneer Probes' Acceleration

On October 5, 1998, the journal Physical Review Letters published, in its volume 81, an article titled:

Indication, from Pioneer 10/11, Galileo, and Ulysses Data, of an Apparent Anomalous, Weak, Long-Range Acceleration.

John D. Anderson, Philip A. Laing, Eunice L. Lau, Anthony S. Liu, Michael Martin Nieto and Slava G. Tuyshev

.....Reference: PACS numbers: 04.80.-y, 95, Eg, 95.55.Pe

.....Below is the abstract, first in English, then its translation into French:

Radio metric data from the Pioneer 10/11, Galileo and Ulysses spacecraft indicate an apparent anomalous, constant, acceleration acting on the spacecraft with a magnitude 8.5 x 10

cm/s

, directed towards the Sun. Two independent codes and physical strategies have been used to analyze the data. A number of potential causes have been ruled out. We discuss future kinematic tests and possible origins of the signal.

Radio signals emitted by the Pioneer 10, Pioneer 11 and Ulysses spacecraft indicate an anomalous acceleration, directed towards the Sun, with an order of magnitude of 8.5 x 10

cm/s

. Two independent calculation programs have been used to analyze the received data. Some potential causes have been eliminated. Future kinematic tests are discussed, as well as the origin of this phenomenon.

Pioneer X

.....A summary of the article follows, with some excerpts.

....The exploration of distant planets began in 72 with the launch of Pioneer 10, followed by Pioneer 11 in 73. After experiencing a gravity assist while crossing Jupiter and Saturn, the two probes took hyperbolic trajectories, thus leaving the solar system. Although Pioneer 10 still transmits signals, NASA officially ended this mission on March 31, 1997, when the probe was at a distance of 67 astronomical units from the Sun. The radio system of Pioneer 11 was shut down on October 1, 1990, when this second probe was at 30 astronomical units from the Sun. Nevertheless, due to their excellent rotational stabilization, these probes are very good devices for dynamic studies. Acceleration measurements (in fact, deceleration) can be performed, spaced over five days, leading to an evaluation precision of ~ 10-10 cm/s2. Therefore, the trajectories of these two spacecraft were analyzed at the JPL (Jet Propulsion Laboratory, within the DSN (Deep Space Network). In this type of analysis, of course, the perturbations due to the planets, radiation pressure, interplanetary medium effects, and general relativity effects were taken into account. In short, all precautions were taken to obtain an analysis result that eliminates all known causes of variations compared to a simple Keplerian trajectory. From 1980, when the radiation pressure effect (which decreases with r-2) could be neglected, which induced, at a distance of 20 astronomical units, an acceleration less than 5 x 10-8 cm/s2, the analyses revealed an abnormal deceleration component, a "sun-directed acceleration" (to use the term used in the article), with a typical value of: (8 ± 3) 10-8 cm/s2. We then considered that this effect could be due to:

• the gravitational field of the Kuiper belt
• the gravitational field of the galaxy
• errors in the ephemerides - typical errors in the evaluation of the Earth's position
• precession and nutation phenomena.

....But none of these "forces" could justify such an effect: there was a difference of three orders of magnitude. It was then imagined that the phenomenon could be due to the power decrease of the electricity generators, using plutonium. But this cause was eliminated, because if it had been the case, the phenomenon would have varied over time according to the power decrease of these on-board electricity sources. Thus, we were led to the conclusion that the probes were subject to a sun-directed acceleration of:

....- ( 8.09 ± 0.20 ) 10-8 cm/s2 for Pioneer 10 ....- ( 8.56 ± 0.15 ) 10-8 cm/s2 for Pioneer 11

....These values did not change, within a sensitivity of 2 10-8 cm/s2, in a distance range from 40 to 60 astronomical units. We then thought about the effect of a drag force, of the action of the viscosity of the surrounding medium, proportional to the speed of the probes. But this was hardly credible, as the trajectories of these two probes are quite different from a radial trajectory, relative to the Sun.

...We then extended our analyses to two other probes: Galileo and the Ulysses probe, whose trajectory is outside the ecliptic plane. Enormous quantities of data were available, concerning Doppler effect measurements. It quickly appeared impossible to extract anything from the data related to the Galileo probe, given the non-negligible effect of radiation pressure, related to the Sun. On the other hand, the analysis of the data concerning Ulysses revealed an unknown acceleration, always directed towards the Sun, worth:

...- ( 12 ± 3 ) 10-8 cm/s2

...Finding the same phenomenon with this third vehicle, we then thought that it could be due to an error related to the code used. We therefore changed the analysis tool by using the CHASMP (Compact High Accuracy Motion Program): no change. We were led to consider that atomic clocks could "drift over time" or even give different values at different points on Earth (...).

...This being said, we found for Galileo the same phenomenon ( 8 ± 3 ) 10-8 cm/s2 : But the proximity to the Sun made this value practically equal to that resulting from the radiation pressure effect (which could, however, be completely neglected by Pioneer 10, Pioneer 11 and Ulysses).

...Then, we thought about an unknown interaction between the photons from the waves and the solar wind (...). The discussion then focused on future missions such as "Pluto Express" and "Solar Probe".

..We wondered if this effect could not be attributable to the presence of dark matter in the solar system but this type of interpretation implied the presence of a quantity of dark matter greater than 3 10-4 solar masses. But this would contradict then the reliability of the precision of the ephemerides, based on the visible mass. One could say that a parasitic mass of two orders of magnitude less would be sufficient to create observable perturbations, including for objects as distant as Uranus. The dark matter track had to be abandoned, as well as the hypothesis of a swarm of "massive neutrinos".

..We then considered modifying the gravitational potential by taking into account the addition of a Yukawa force. The reference is:

..M.M Nieto and T Goldman, Phys. Rev. Rep. 205 , 221 (1991) ; 216 , 343 (1992).

..The gravitational potential then becomes:

l is the radius of action of this new force. This type of model leads to a constant acceleration:

where a1 is the Newtonian acceleration at the distance r1 = one astronomical unit. We also considered other models where Newton's law is modified. However, this modification of Newton's law should then have an influence on the orbits of the planets of the solar system. For planets like Mars, Viking probes are able to detect orbital parameter variations of the order of hundreds of meters. By combining the effects that both Mars and Earth would undergo, the measurement precision would then be 150 meters. Now:

The Pioneer effect is not seen.... a large error here would cause inconsistencies with the overall planetary ephemeris.

Translation: "The Pioneer effect is not observed.... a large error here would be inconsistent with the overall planetary ephemeris."

...The consequence: if this modification of Newton's law had an effect on the trajectories of Mars and Earth (therefore had a pretension of universality), the constraints imposed by the precision of the Viking measurements mean that the effect should be less than 0.1 10-8 cm/s2 .

..*.**Consequently, if the anomalous radial acceleration acting on spinning spacecraft is gravitational in origin, it is not universal. That is, it must affect bodies in the 1000 kg range more than bodies of planetary size by a factor of 100 or more. This would be a strange violation of the Equivalence Principle. *

Translation: Consequently, if the anomalous radial acceleration observed for spinning spacecraft had a gravitational origin, it would not correspond to a new universal law. Indeed, this would mean that the effect would be more significant for objects with a mass of the order of a ton than for objects as massive as planets, by a factor of about 100.

...Incidentally, note that the Viking data were also analyzed with a second code (CHASMP), already mentioned above.

...The conclusion of the article: the cause of the effect remains a complete mystery for now. Of course, one then wants to wonder if such an effect, although weak, albeit perfectly measurable, could not be due to the repulsive effect of a twin matter environment, which tends, at all scales, to infiltrate everywhere where matter is absent. According to my model, the "interstellar vacuum" would contain (in the adjacent universe relative to ours) a density of twin matter much higher than the density of matter that has become very rarefied. A systematic study, a modeling, computer simulations would constitute a very nice thesis topic. Unfortunately, the poor graduate student who would venture into such waters would immediately see his research career obliterated, definitively.

Remy Chauvin is the author of a sentence that will serve as a conclusion:

...When one wants to undertake something, one immediately has against oneself:

...........- The people who do the same thing

...........- Those who do the opposite

*...........- Those who do nothing. *

A note in passing: One could think (a detail not mentioned in the article) that this anomalous acceleration effect could be related to a "cosmological constant effect". However, since the observed effect acts in the direction of a deceleration, one should then speak of "attractive power of the vacuum". Moreover, this effect should increase with distance. Now, the Pioneer probes, or at least one of them, are at about 60 astronomical units, that is, 1013 meters from the Sun. By placing the (average) orbit of Pluto at five billion kilometers, that is, 5 1012 meters, we see that these probes, whose oldest was launched in 72, are at twice the diameter of the solar system. On the other hand, the Ulysses probe, which ascends into the cosmos outside the ecliptic plane, only reaches three hundred million kilometers, that is, one tenth of Uranus' orbit, or one sixth of Pluto's orbit. Ulysses is therefore much closer to the Sun. However, the constant acceleration anomaly observed for Ulysses is 12 10-8 cm/s2, that is, 1.4 times more significant than the anomalies observed for the Pioneer probes. This seems to exclude a priori the "cosmological constant" track.

...What about an effect related to a repulsive twin matter environment? In this perspective, given that matter and twin matter repel each other, where one dominates, the other is absent, and vice versa. In the scheme I indicated, large conglomerates of twin matter would be located at the centers of the "large voids" constituting the large-scale structure of the universe (VLS). Matter would then be arranged near structures resembling "jointed soap bubbles", the galaxy clusters being the junction points of three sheets. In these "sheets": galaxies, bathed in a twin matter environment, structured like a sort of gruyère, the galaxies being nestled in the voids. But all of this remains schematic. Twin matter tends to infiltrate everywhere it can. A galaxy is not a uniform distribution of matter. With respect to stellar populations, they are tiny grains of matter populating vast voids. In these voids, there are interstellar gas clouds, certainly. But matter is not omnipresent. Where it is in a rarefied state, twin matter infiltrates. One can therefore imagine that interstellar space could contain twin matter, at low density. This would then contribute to the "confinement" of the system, but minimally. The solar system, with respect to gravity, can be figuratively represented by a point mass: that of the Sun, 2 1030 kilograms. With respect to this mass, the planets are only small perturbing objects. Consequently, if there is a distribution of twin matter, it would, at first order, have a distribution possessing a quasi-spherical symmetry. Between the stars, far from the Sun, this twin matter would have a density r* almost constant, which would decrease when approaching the Sun. It is this lack that, having a confining effect, would slow down the space probes. This distribution would need to be evaluated using numerical simulations and then see if such an interpretation would be compatible with the precision of the ephemerides.

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