twobyfour said:

“An order of 100k km (386000, to be more precise) a small deviation? I guess it is a matter of opinion.”

We maybe talking about different things. The Pioneer Anomaly represents an error of about 400 km.

“Magnetism? Just hanging out there like that?”

It’s believed the “Pioneer Anomaly” and the “Flyby Anomaly” are due to the same physical phenomena. The basic phenomena is the spacecraft’s trajectory is modified by two different gravitational fields as the vehicle flies along a hyperbolic trajectory. In the case of the Flyby Anomaly the two gravitational fields are the Sun’s (which can be thought of as fixed in inertial space) and the Earth’s (which is moving with respect to the Sun). If you move a charged particle then it produces a magnetic field. The magnetic analog to gravity would be the Earth’s gravitational field moving with respect to the Sun’s.

The trajectory variations seen with the Pioneer Anomaly are so small that people can provide arm waving explanations, e.g. one side of the spacecraft was warmer than the other due to the radioactive thermal generators (RTGs) thus causing a photon pressure imbalance. However there really are no simple arm waving explanations for the Flyby Anomaly.

twobyfour said:

“Re: Solar system stable. Bare the instances of instability, it has been stable.”

“Stability” in this context means the actual planetary trajectories are more or less conic section trajectories and the system isn’t chaotic. It so happens that 3-body and N-body systems can be chaotic. No one has proven that the planetary trajectories of the Solar System are not chaotic. Of course it’s a pretty safe bet that the Solar System must be fairly stable or we wouldn’t be having this discussion.