Towards a new era in giant exoplanet characterisation

TL;DR

This paper emphasizes the importance of precise age and atmospheric metallicity measurements from upcoming space missions like Plato, Ariel, and JWST to improve the accuracy of giant exoplanet composition determination.

Contribution

It demonstrates how accurate stellar ages and atmospheric metallicities can significantly reduce uncertainties in giant exoplanet bulk composition estimates.

Findings

Accurate stellar ages can halve the uncertainty in bulk-metallicity estimates.

Atmospheric metallicity measurements can reduce uncertainty by a factor of four to eight.

Upcoming missions will enable more precise characterization of giant exoplanets.

Abstract

Determining the composition of giant exoplanets is crucial for understanding their origin and evolution. However, the planetary bulk composition is not measured directly but must be deduced from a combination of mass-radius measurements, knowledge of the planetary age and evolution simulations. Accurate determinations of stellar ages, mass-radius, and atmospheric compositions from upcoming missions can significantly improve the determination of the heavy-element mass in giant planets. In this paper, we first demonstrate the importance of an accurate age measurement, as expected from Plato, in constraining the planetary properties. Well-determined stellar ages can reduce the bulk-metallicity uncertainty up to about a factor of two. We next infer the bulk metallicity of warm giants from the Ariel mission reference sample and identify the Ariel high-priority targets for which a measured atmospheric metallicity can clearly break the degeneracy in the inferred composition. We show that knowledge of the atmospheric metallicity can broadly reduce the bulk-metallicity uncertainty by a factor of four to eight. We conclude that the accurate age determination from Plato and atmospheric measurements by Ariel and the James Webb Space Telescope will play a key role in revealing the composition of giant exoplanets.