How common is plate tectonics for terrestrial planets and exo-planet terrestrials? Mercury has a strong magnetic field, and hence probably a circulating fluid. Yet no evidence of plate tectonics? And no tectonic evidence for Mars.
What about Venus? Perhaps ground penetrating radar from orbit, looking for a subduction plate. A combination of higher frequency radar for better resolution, and lower frequency for deeper penetration? Also perhaps oblique angulated radar imaging, and then a processed composite, for better slab visualization? Is this possible with present technology?
In principle, might there be a critical mass required for tectonics; such as consistent with earth’s mass/energy, enhanced from collision with a planetesimal?