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Exoplanet Climatology [Mayne 2021]

Exoplanet Climatology

Supervisor: Professor Nathan Mayne

The Exeter Exoplanet Theory Group (EETG, exoclimatology.com) is a multidisciplinary research group focused on the study of planetary climates. Our work combines state-of-the-art numerical models with cutting-edge observational data to attack puzzles spanning gas giant and terrestrial or rocky exoplanets. Much of our work involves close collaboration with the UK Met Office, through shared software development, and interaction/exchange of people and knowledge.

Current research of the EETG focuses on both terrestrial or rocky exoplanets, and gas giants, as well as solar systems. The exact focus of this PhD is flexible, but example areas are detailed below. 

For gas giant exoplanets, observations indicate a range of atmospheric states from cloudy to hazy to clear (Sing et al., 2016). Currently, no clear trends with basic planetary properties, and the presence of clouds is apparent, and a vast array of models are being used to interpret the data and explore this complex issue. At the EETG we have developed a hierarchy of numerical tools, from 1D retrieval frameworks to fully coupled radiative-chemical-cloud-dynamics 3D Global Circulation Models (GCMs). For the GCM detailed microphysical cloud models, and more simple parameterised cloud treatments have been developed, but neither of these treatments has included a consistent treatment of the potential photochemistry. Although photochemical pathways are complex, precursor species can be used to determine where photochemical products, i.e. hazes, may develop.

The next set of exoplanet observation facilities, such as ARIEL and the JWST will not only improve observations of our most observable candidate exoplanets, short period planets termed hot Jupiters, but also extend to smaller planets in more distant orbits, mini-Neptunes, as detected by, for example, TESS. Our current numerical frameworks have been applied mostly to hot Jupiters, but recent work (Mayne et al., 2019, Wordsworth et al., 2020) has demonstrated that mini-Neptune planets may require a more detailed exploration of the dynamical state of the atmosphere.

Finally, for terrestrial planets, a huge number of questions remain. The primary goal for our group is to identify the key physical processes which dominate the climatic state of these planets, and explore how these processes behave differently or similarly to Earth. Sergeev et al., (2020), Eager et al., (2019) and Boutle et al. (2020), for example, explore the impact of convection, stellar spectrum and airborne mineral dust on the climate of tidally-locked terrestrial planets. Given the vast range of potential atmospheric compositions, significantly more study is required to determine what the key ‘tipping points’ are between various climatic states, alongside the inclusion of new model elements, for example treatments of ocean heat transport.

Environment & Skills: In this PhD project you would join a diverse group studying a range of exoplanet, solar system planet and Earth, climate problems. Access to ample high-performance-computing resources is available, alongside opportunities for training through the Met Office and University of Exeter’s training programmes. The successful candidate will have experience in programming (no specific language required but fortran and python are desirable), and an undergraduate degree in mathematics, physics or related discipline at UK 2:1 level or higher (or international equivalent).