摘要：AbstractTo better understand Earth's present tectonic style–plate tectonics–and how it may have evolved from single plate (stagnant lid) tectonics, it is instructive to consider how common it is among similar bodies in the Solar System. Plate tectonics is a style of convection for an active planetoid where lid fragment (plate) motions reflect sinking of dense lithosphere in subduction zones, causing upwelling of asthenosphere at divergent plate boundaries and accompanied by focused upwellings, or mantle plumes; any other tectonic style is usefully called “stagnant lid” or “fragmented lid”. In 2015 humanity completed a 50+ year effort to survey the 30 largest planets, asteroids, satellites, and inner Kuiper Belt objects, which we informally call “planetoids” and use especially images of these bodies to infer their tectonic activity. The four largest planetoids are enveloped in gas and ice (Jupiter, Saturn, Uranus, and Neptune) and are not considered. The other 26 planetoids range in mass over 5 orders of magnitude and in diameter over 2 orders of magnitude, from massive Earth down to tiny Proteus; these bodies also range widely in density, from 1000 to 5500 kg/m3. A gap separates 8 silicate planetoids withρ = 3000 kg/m3or greater from 20 icy planetoids (including the gaseous and icy giant planets) withρ = 2200 kg/m3or less. We define the “Tectonic Activity Index” (TAI), scoring each body from 0 to 3 based on evidence for recent volcanism, deformation, and resurfacing (inferred from impact crater density). Nine planetoids with TAI = 2 or greater are interpreted to be tectonically and convectively active whereas 17 with TAI <2 are inferred to be tectonically dead. We further infer that active planetoids have lithospheres or icy shells overlying asthenosphere or water/weak ice. TAI of silicate (rocky) planetoids positively correlates with their inferred Rayleigh number. We conclude that some type of stagnant lid tectonics is the dominant mode of heat loss and that plate tectonics is unusual. To make progress understanding Earth's tectonic history and the tectonic style of active exoplanets, we need to better understand the range and controls of active stagnant lid tectonics.Graphical abstractDisplay OmittedHighlights•Planetoids include 26 planets, moons, dwarf planets, and Kuiper belt objects >500 km diameter with surfaces observed from space probes.•Planetoids include 18 icy bodies (density <2.3 g/cc) and 8 rocky bodies (density = 3.0 to 5.6 g/cc).•Tectonic Activity Index based on volcanism, faults, and impacts is used to classify planetoids into 9 active and 17 dead bodies.•Stagnant lid tectonics contrasts with plate tectonics by consisting of a single lithospheric plate.•Nearly all active and dead planetoids are characterized by stagnant lid; only Earth has plate tectonics.
