Abstract

Thousands of exoplanets have now been discovered with a broad range of masses, sizes and orbits: from rocky Earth-size planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. Work in exoplanet spectroscopy with current instruments has thus far been very piecemeal and mainly focused on gaseous planets. 

The launch of the James Webb Space Telescope next year will permit for the first time the remote exploration of smaller planets: super-Earths and sub-Neptunes. However, progress with the science questions spelled out above demands a very large, unbiased spectroscopic survey of exoplanets. In the next decade new dedicated space missions, such as the ESA’s next medium-class science mission ARIEL ,  have been conceived to conduct such a survey and to explore the nature of exoplanet atmospheres and, through this, the key factors affecting the formation and evolution of planetary systems in our galaxy.