The composition of transiting giant extrasolar planets

TL;DR

This paper analyzes the composition of transiting giant exoplanets by comparing mass and radius measurements, confirming that planets around metal-rich stars tend to have more heavy elements, despite uncertainties in planetary physics.

Contribution

It extends previous analyses to a larger sample of 18 transiting planets, confirming the correlation between host star metallicity and planetary heavy element content.

Findings

Planets around metal-rich stars have more heavy elements.

Uncertainties in planetary physics affect composition estimates.

The correlation between stellar metallicity and planetary heavy elements is confirmed.

Abstract

In principle, the combined measurements of the mass and radius a giant exoplanet allow one to determine the relative fraction of hydrogen and helium and of heavy elements in the planet. However, uncertainties on the underlying physics imply that some known transiting planets appear anomalously large, and this generally prevent any firm conclusion when a planet is considered on an individual basis. On the basis of a sample of 9 transiting planets known at the time, Guillot et al. A&A 453, L21 (1996), concluded that all planets could be explained with the same set of hypotheses, either by large but plausible modifications of the equations of state, opacities, or by the addition of an energy source, probably related to the dissipation of kinetic energy by tides. On this basis, they concluded that the amount of heavy elements in close-in giant planets is correlated with the metallicity of the parent star. Furthermore they showed that planets around metal-rich stars can possess large amounts of heavy elements, up to 100 Earth masses. These results are confirmed by studying the present sample of 18 transiting planets with masses between that of Saturn and twice the mass of Jupiter.