Gravity Ruled Out as the Cause of the Pioneer Anomaly
If the strange deceleration of the Pioneer spacecraft is caused by gravity, then it should also act on other bodies in the outer solar system. That doesn’t seem to be the case.
The Pioneer anomaly is an unexplained deceleration of the Pioneer
10 and 11 spacecraft that seems to be acting on them as they head out
of the Solar System. This deceleration is tiny: just
(8.74±1.33)×10^−10 ms^−2. The big question is where does it
come from.
One possibility is that the deceleration is the result of some
long range gravitational force that is not observed on Earth. But if
that’s the case, then this force should act on all of the many
objects in the outer Solar System.
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Earlier this year, we
looked at one study of the orbit of Pluto which was unable to
rule out the possibility that a Pioneer-like force acts on it because
Pluto’s orbit is so poorly known.
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Today we look at a similar study in which the objects of attention
are the major Neptunian satellites: Triton, Nereid and Proteus.
Earlier this year, astronomers published the result of a new analysis
of the motion of these bodies taken over several orbits.
Now Lorenzo Iorio, at the Istituto Nazionale di Fisica Nucleare in
Pisa, Italy, has analysed these orbits and concludes that a
Pioneer-like force cannot be acting on Triton, Nereid and Proteus
because the resulting anomalous perturbations would be too large to
have escaped detection.
“The possibility that the Pioneer anomaly may be an exotic
gravitational phenomenon seems to be challenged,” says Iorio.
This work is part of a growing body of evidence that the Pioneer
anomaly is not a gravitational effect.
That’s a puzzle. If not gravitational in origin, what kind of
force is acting on the Pioneer spacecraft?
Ref: arxiv.org/abs/0912.2947: Does the Neptunian System of Satellites Challenge a Gravitational Origin For The Pioneer Anomaly?
