Formation and composition of planets around very low mass stars

TL;DR

This study models planet formation around very low mass stars, predicting their size and water content, and shows that volatile-rich, Earth-sized planets can form close-in within the core accretion framework.

Contribution

It introduces detailed planetary formation and composition models specific to very low mass stars, highlighting the importance of disk properties and longevity.

Findings

Planets can form at small orbital periods around low mass stars.

Planet radii are peaked at about 1 Earth radius.

Planets are generally volatile-rich, especially with long-lived disks.

Abstract

The recent detection of planets around very low mass stars raises the question of the formation, composition and potential habitability of these objects. We use planetary system formation models to infer the properties, in particular their radius distribution and water content, of planets that may form around stars ten times less massive than the Sun. Our planetary system formation and composition models take into account the structure and evolution of the protoplanetary disk, the planetary mass growth by accretion of solids and gas, as well as planet-planet, planet-star and planet-disk interactions. We show that planets can form at small orbital period in orbit about low mass stars. We show that the radius of the planets is peaked at about 1 rearth and that they are, in general, volatile rich especially if proto-planetary discs orbiting this type of stars are long-lived. Close-in planets orbiting low-mass stars similar in terms of mass and radius to the ones recently detected can be formed within the framework of the core accretion paradigm as modeled here. The properties of protoplanetary disks, and their correlation with the stellar type, are key to understand their composition.