Spectra from Earth-like planets

Spectra from different Earth-like planets
Credit: ESA

Radiative and photochemical processes in terrestrial exoplanets

Supervisor: Dr Eric Hébrard

The recent discovery of the TRAPPIST-1 system shows that the characterisation of small, rocky exoplanets is within reach, particularly around low-mass stars. The NASA Transiting Exoplanet Survey Satellite (TESS, launched in April 2018) will identify even small exoplanets orbiting bright stars with a range of stellar types. The idea that those distant new worlds could harbour life is fascinating and provides a strong motivation to improve our understanding of the atmospheric processes which may play a role on the emergence of life and/or could affect the detection of biosignatures revealing its presence. Among those processes, radiation and photochemistry, namely the study of how molecules and atoms interact with light to influence the atmospheric structure and composition, is a major one in planetary atmosphere modelling.

This project is devoted to the study of the radiative and photochemical processes in planetary atmospheres, with applications specifically to terrestrial exoplanets. Current observation techniques, along with the soon-to-launch James Webb Space Telescope (JWST), favour the detection of hot and/or bright exoplanets. With the discovery of ever smaller and colder exoplanets, and their possible characterisation with the Extremely Large Telescope (ELT), terrestrial worlds with cloudy/hazy atmospheres will have to be increasingly considered. Radiative and photochemical processes, including the properties of chemical haze and/or clouds, are playing a key role on the atmospheric structure and composition and on the spectroscopic signatures of these planets. Taking those processes into account is of key importance, not only for the characterization of potential biosignatures on the future Earth 2.0, but also for the general understanding of exoplanet atmospheres and the interpretation of present and future observations.

The Astrophysics group at the University of Exeter is currently at the forefront of exoplanetary detection and atmosphere modelling and has recently developed state-of-the-art tools to address these issues. ATMO is a flexible 1D radiative-convective chemical kinetic model including a complete treatment of radiative transfer as well as sophisticated and versatile chemical networks. ATMO has already been applied successfully to the atmospheres of brown dwarfs and hot Jupiters but it still lacks the ability to model the atmospheric chemistry of terrestrial planets. Also, the UK Met Office Unified Model (UM), a General Circulation Model (GCM) usually used to predict Earth's weather and climate, has been adapted for the study of both Earth-like and gas giant exoplanets. This project will mainly involve the use of these local state-of-the-art tools and their further adaptation to modelling a large variety of terrestrial planets and simulate their possible future observations.

The required background for the student is primarily in physics and mathematics. Backgrounds in chemistry and/or numerical simulations are welcome, but not mandatory.

For more details on this project please contact Dr Eric Hébrard.