And finally Eros, an asteroid which is rapidly replacing Venus as the best mapped body in the solar system. It has unique features including boulders 60-70m high on steep sloping surfaces and very jumbled terrain. How these features originated in an environment of such low gravity will keep scientists very busy developing explanations. Overall there is evidence for three possible tectonic mechanisms at work within the solar system. Collision appears to have reworked the surface of Miranda.
Tidal drag is in the process of reworking the surface of Io.
Internal heat engines drive or have driven surface activity on Earth and Mars. For the present, Earth still remains the only rocky planet with existing proven plate tectonic activity being driven by an internal heat engine.