In message , alistair
writes
Dark energy could be causing the anomalous acceleration of pioneer
10.
The solar system is surrounded by the spherical Oort cloud.If dark
energy consists of particles that flow into the galaxy, the Oort
cloud
would shield
the solar system from those particles.However a gap in the Oort cloud
would allow some dark energy particles to flow into the solar system.


ANDRE?MICHAUD wrote:

There are a few problems with this idea :-)

The paper by Anderson et al. which everyone cites is available online
at
http://xxx.lanl.gov/abs/http://www....gr-qc/0104064. It has figures
for the mass of
the Pioneers (223 kg dry mass) and their surface area (or at least
that
of the dish antenna, which accounts for nearly all of it. It's a 2.74
meter dish giving an area of 5.9 square meters.
Also, the two Pioneers are going in nearly opposite directions.


ALISTAIR writes:

The mass and surface area you quote for Pioneer 10 would give an
acceleration for Pioneer 10 that is roughly only one third smaller
than the figure I calculated of 10^ -12 m/s^2.The correct figure NASA
gives is 10^-10 m /s^2.
However, if dark energy consists of particles with rest mass and these
particles in our part of the Milky Way move at 99.9999 per cent the
speed of light then there would be a relativistic mass increase by a
factor of 10000 compared to the average expectation for dark energy
mass which would have to be moving at a speed of around 1/3 that of
light.Whether or not dark energy actually has a different mass density
in galaxies compared to intergalactic space,I couldn't say.There is
also the possibility that dark energy coming through a gap in the Oort
cloud could pick up speed and mass if it has fluid like properties (
though I think such a Bernouilli flow is unlikely given how large the
mass increase would be).Both these factors could give the acceleration
NASA quotes.The fact that the Pioneers are moving in opposite
directions is irrelevant because the Oort cloud could have other gaps
in it which allow dark energy particles into the solar sytem.