The global tectonics of planets

It is noted that tectonic activity currently occurs on the earth and Venus (plate tectonics), Io (global volcanism), Enceladus, and possibly Rhea and Iapetus (ice tectonics with tidal heating). The relicts of ancient global tectonics are obvious on Mars, noticeable on the moon, Ganymede, and Tethys, and apparently exist on many other planets. It is likely that all the aforementioned planets passed through a stage of gravitational differentiation of the interior; it is not excluded that this stage has always been accompanied by mantle convection and the tectonics of lithospheric plates. Finally, it is suggested that radioactive heating always played a secondary role, while tidal heating sometimes played a primary role on certain planets (especially Io).