Unlocking Rocky Exoplanet Atmospheres via Next-Generation Stellar Characterisation

One of the most significant research directions in modern astronomy is the search for atmospheres on rocky planets orbiting other stars. Establishing the prevalence of thick atmospheres on extrasolar rocky worlds is a frontier with profound implications for understanding planetary formation, atmospheric chemistry, and the habitability of terrestrial worlds throughout our galaxy. With the powerful spectroscopic capabilities of the James Webb Space Telescope (JWST), we finally have the sensitivity to characterise rocky exoplanet atmospheres.

The rocky exoplanets JWST is now observing generally orbit M Dwarf stars, due to the significantly higher signal-to-noise ratio compared to larger Sun-like stars. However, M Dwarf stars pose many challenges to atmospheric retention for close-in rocky exoplanets, due to their extreme-UV radiation and frequent flaring. Consequently, these worlds have experienced a significantly different stellar history and irradiation environment compared to the solar system. A further complication in searching for rocky planet atmospheres around M Dwarf stars arises from stellar surface inhomogeneities (e.g. starspots). These surface inhomogeneities can imprint spectral signatures in exoplanet spectra that can mimic or overwhelm atmospheric absorption features. Our drive to detect rocky exoplanet atmospheres is therefore confronted by our limited ability to accurately model the emergent spectra of M Dwarf stars.

This project will extend a state-of-the-art Bayesian modelling code to model JWST spectra of M Dwarfs and their orbiting rocky worlds. You will develop a new framework for jointly inferring properties of rocky exoplanets and their host M Dwarf stars. Alongside your model development, you will have access to cutting-edge JWST observations of some of the highest-profile rocky exoplanet systems, including spectra of the TRAPPIST-1 system, through joining several international collaborations. The ultimate goal of your project will be to enrich our understanding of M Dwarf active regions and search for clear evidence of rocky exoplanet atmospheres.

As a PhD Candidate, you will have the opportunity to use your ingenuity and passion to make major advances in exoplanetary science. This project will enable you to become a leader at the interface of theoretical and observational astronomy and at the intersection of stellar and exoplanet astronomy. You will become an expert in some of the most important foundational techniques of modern astrophysics, including radiative transfer, Bayesian analysis, and high-performance computing. By the end of your PhD, you will be a highly proficient astrophysicist equipped with the knowledge and skills to formulate and pursue your own independent research directions.

Further reading: 

• Rackham et al., 2023, The Effect of Stellar Contamination on Low-resolution Transmission Spectroscopy: Needs Identified by NASA’s Exoplanet Exploration Program Study Analysis Group 21 – RASTI, 2, 148.
• Moran et al., 2023, High Tide or Riptide on the Cosmic Shoreline? A Water-rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ 486b from JWST Observations – ApJL, 948, L11.
• MacDonald, 2023, POSEIDON: A Multidimensional Atmospheric Retrieval Code for Exoplanet Spectra – JOSS, 8(81), 4873
• Madhusudhan, 2018, Atmospheric Retrieval of Exoplanets – Springer, Handbook of Exoplanets

Further opportunities and support:

• Weekly supervision meetings to guide your development as an astrophysics researcher.
• Become a core member of the new exoplanet atmospheres research group at St Andrews and join the St Andrews Centre for Exoplanet Science.
• Participation in several international collaborations with access to JWST observations of rocky exoplanets.
• Opportunities to collaborate with other professional astronomers at St Andrews with expertise in exoplanetary and stellar astrophysics.
• Become an expert in Python programming, data science, and Bayesian analysis techniques.
• Access to high-performance computing (HPC), including a newly-operational state-of-the-art computing cluster.
• Weekly exoplanet journal club, astronomy lunch talks, and full department colloquia from leading international speakers.
• Daily departmental coffee and tea.
• Training through the Scottish Universities Physics Alliance, giving access to a wide range of astronomy and data science courses delivered by experts from across Scotland.
• A wide range of high-quality transferable skills workshops delivered by the professional student and staff developers at the University of St Andrews, including presentation skills, scientific writing, leadership, management skills, and entrepreneurship.
• The opportunity to present your research at national and international conferences and to travel abroad for collaboration purposes.

Entry Requirements: At least a UK 2:1 honours degree in a relevant subject, or its international equivalent. 

Closing date: 1st February 2025 for standard admissions, but later applications may be considered until the position is filled.

Funding: The School of Physics and Astronomy at the University of St Andrews has a range of funding opportunities for both UK and international students. For more information please visit https://www.st-andrews.ac.uk/physics-astronomy/prospective/pgr/. UK research council funding (STFC) is awarded on an annual basis, so you should apply before the deadline given above to be considered for this type of funding. 

How To Apply: please visit https://www.st-andrews.ac.uk/physics-astronomy/prospective/pgr/ to find further information on applying for this project. 

Applications should include:

• 1-page personal statement using the template provided on the School of Physics & Astronomy webpage (https://www.st-andrews.ac.uk/physics-astronomy/prospective/pgr/)
• 1-2 page Curriculum Vitae
• Two reference letters
• Degree transcripts and certificates
• Proof of English language proficiency, if required
• For further information on the application process please contact physpg@st-andrews.ac.uk