Super-Earths: Atmospheric Accretion, Thermal Evolution and Envelope Loss

Combined mass and radius observations have recently revealed many short-period planets a few times the size of Earth but with significantly lower densities. A natural explanation for the low density of these super Earthsplanetsuper-Earth is a voluminous gas atmosphere that engulfs more compact rocky cores. Planets with such substantial gas atmospheres may be a missing link between smaller planets, that did not manage to obtain or keep an atmosphere, and larger planets, that accreted gas too quickly and became gas giantsgiant planetgas-. In this chapter we review recent advancements in the understanding of low-densitydensitylow- super-Earth formation and evolution. Specifically, we present a consistent picture of the various stages in the lives of these planets: gas accretion from the protoplanetary disk, possible atmosphere heating and evaporation mechanisms, collisions between planets, and finally, evolution up to the age at which the planets are observed.