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.
Dark energy accounts for up to 70 per cent of the mass of the universe
and the universe has an approximate average mass density of 10 ^ -27
kg/ m^3.So, as an approximation, dark energy has a mass density of
about
10 ^ -27 kg/ m^ 3 too.If dark energy particles move at close to the
speed of light then 10 ^ -27 kg of them will move through one metre in
10 ^ -8 seconds. The particles will have a total momentum of 10 ^ -27
x 10 ^ 8 = 10 ^ -19.
The maximum force the particles can exert in 10 ^ -8 seconds on one
square metre of pioneer 10 is given by Force = rate of change of
momentum / time
Force = (10 ^ -19 minus 0 ) / 10 ^ - 8 = 10 ^ -11 Newtons.
Now assuming pioneer 10 has an area facing the direction of travel of
the dark energy particles through the Oort cloud and that area is at
most 100 square metres (perhaps someone on sci.physics.research knows
the exact area!)
then the total force on pioneer 10 due to dark energy is 10 ^ -11 x
100 Newtons = 10 ^ - 9 Newtons.Since acceleration = force / mass and
assuming pioneer 10 has a mass of about 1000 kg ( again, perhaps
someone on sci.physics.research can put an exact figure to this), then
the acceleration of pioneer 10 towards the sun caused by dark energy
particles would be about
10 ^ - 9 / 1000 = 10 ^ -12 m / s ^2.The figure Nasa gives is 10 ^ -10
m / s ^2.
If the exact mass and area of pioneer 10 are used, the answer given
for the acceleration of pioneer 10 due to dark energy flowing through
a gap in the Oort cloud could well be a lot closer to the value Nasa
gives.