Composition of Ices in Low-Mass Extrasolar Planets

TL;DR

This study models the formation and composition of ices in icy planetesimals of low-mass extrasolar planets, revealing that initial gas composition influences ice makeup more than disk temperature.

Contribution

It introduces a comprehensive model for icy planetesimal composition considering various formation conditions and initial gas phase compositions.

Findings

Ice composition weakly depends on disk thermodynamics

Initial gas phase composition significantly influences ice makeup

Model applicable to diverse planetary systems

Abstract

We study the formation conditions of icy planetesimals in protoplanetary disks in order to determine the composition of ices in small and cold extrasolar planets. Assuming that ices are formed from hydrates, clathrates, and pure condensates, we calculate their mass fractions with respect to the total quantity of ices included in planetesimals, for a grid of disk models. We find that the composition of ices weakly depends on the adopted disk thermodynamic conditions, and is rather influenced by the initial composition of the gas phase. The use of a plausible range of molecular abundance ratios and the variation of the relative elemental carbon over oxygen ratio in the gas phase of protoplanetary disks, allow us to apply our model to a wide range of planetary systems. Our results can thus be used to constrain the icy/volatile phase composition of cold planets evidenced by microlensing surveys, hypothetical ocean-planets and carbon planets, which could be detected by Corot or Kepler.