In dealing with electricity, we usually refer to Earth as the electrical neutral or ground. Is there any evidence that other planets' ground is at the same electrical potential level as the Earth's?
If somehow, there was a lossless conductive connection between two planets, would current flow accros It? Would this be theoretically a source of energy?
I dunno how or why a planet would have a significant net charge, but supposing it did, here's some initial calculations.
If the planets have a different net charge, you can treat them as capacitor plates.
Capacitance in its simplest form is
$C = \frac{\epsilon *A}{d}$
The permittivity $\epsilon$ of vacuum space is 8.85 x 10-12 farad per meter .
Let's choose a nearby (nonexistent) planet at 5 LY = 5 * 9.461e+15 m .
Looks like the capacitance is pretty close to zero. So the energy available,
$E = \frac{CV^2}{2}$ is going to be nonexistent unless there's a seriously large voltage.
