Super-Earths: Properties and Tectonics

Super-Earths are the newest class of discovered extra-solar planets, and owing to their relative small masses (1-10 M_Earth), they have the potential to resemble Earth. In particular, their thermal state, which is influenced by their tectonic state, is of critical importance when determining if they are habitable. We present results that show that super-Earths have more propitious conditions than Earth to maintain plate subduction, an essential part of plate tectonics. We examine a family of super-Earths of the same age (as expressed by the same Urey ratio) and same surface temperature as Earth, and find that the ratio of driving force to plate resistance increases with mass. This is due to an increase in convective stresses and decrease in plate thickness with mass, expressed by increasing Rayleigh numbers.

In addition, despite the higher gravities, super-Earths exhibit the same plate's pressure-temperature structure, because the increase in gravity is offset by the decrease in plate thickness. With the same plate structure, the deformation mechanisms that occur on Earth might well occur on more massive planets. We investigate two cases: a coulomb failure criterion and a constant yield stress. We find that in both cases, super-Earths have more favorable conditions to deform the plate and maintain subduction.

In summary, terrestrial super-Earths and Earth are very likely to have similar tectonics; and if water is present, they may have similar geochemical cycles. Planned space telescopes (such as JWST) may reveal atmospheric components indicative of a similar planetary environment.