Inevitability of plate tectonics on super-earths

The recent discovery of super-Earths (masses <= 10 M(circle plus)) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planet's thermal evolution and surface conditions. On Earth, plate tectonics has been proposed as a necessary condition for life. Here we show that super-Earths will also have plate tectonics. We demonstrate that as planetary mass increases, the shear stress available to overcome resistance to plate motion increases while the plate thickness decreases, thereby enhancing plate weakness. These effects contribute favorably to the subduction of the lithosphere, an essential component of plate tectonics. Moreover, uncertainties in achieving plate tectonics in the 1 M(circle plus) regime disappear as mass increases: super-Earths, even if dry, will exhibit plate tectonic behavior.