Planetary Magnetic Fields

As might be expected of generators, the magnetic field strengths of the planets is determined mostly by their size; less so by their speed of spin.

Thus those of Mercury and Pluto are weak through small size, and Venus through very slow reverse spin.

Plate tectonic activity of the inner rocky planets appears to be another product of electromagnetic performance. The signs on Mars are not as well defined on Earth, such that professionals consider it to be no longer functioning. More likely is that its smaller size limits the action.

Opinion differs as to whether Mercury shows faint signs; not surprising in view of its miniscule size and resultant, tiny, magnetic field.

Venus, with its low field and reverse spin, predictably shows no evidence of continental drift as with the gas planets, of course. Nonetheless any rocky cores may be expected to follow the rule of size and electrical generation.