Dr Subhajit Sarkar

Publication

• Date
• Type

Research

Research Vision

My research aims to understand how planetary atmospheres can be used to answer two of the most fundamental questions in modern astronomy: How common is life in the Universe? and How do planetary systems form and evolve? By combining observations from the James Webb Space Telescope (JWST) with the development of future space missions, atmospheric modelling, and statistical inference, I seek to establish exoplanet atmospheres as a powerful tool for comparative planetology and astrobiology.

1. Searching for Life Beyond the Solar System

Atmospheric characterisation of temperate worlds

A major focus of my research is the atmospheric characterisation of temperate and habitable-zone exoplanets, particularly sub-Neptunes and proposed Hycean worlds. Through collaborations with the Institute of Astronomy, University of Cambridge, I am a Co-Investigator on two major JWST observing programmes that use NIRISS, NIRSpec, and MIRI spectroscopy to study the atmospheres of temperate sub-Neptunes, including K2-18 b and a sample of potential Hycean candidates. These observations provide an unprecedented opportunity to investigate the chemistry, climate, and potential habitability of planets occupying a previously inaccessible region of parameter space.

Biosignatures and atmospheric modelling

Observations alone cannot establish the presence of life without robust theoretical frameworks. My research therefore develops atmospheric and statistical models to interpret biosignatures and quantify their significance. I am particularly interested in determining how atmospheric observations can constrain the frequency of life-bearing worlds—the fL term in the Drake Equation. This includes developing statistical frameworks, such as those presented in my MNRAS paper on the DRAKE mission concept, together with atmospheric models that improve our understanding of biosignature production, preservation, and detectability.

2. Explaining the Diversity of Planetary Atmospheres

Comparative atmospheric studies with JWST

I use JWST observations to investigate the physical and chemical processes that shape exoplanet atmospheres across a broad range of planetary environments. Alongside observational programmes targeting temperate sub-Neptunes, I develop analysis tools for extracting atmospheric spectra from JWST observations. This includes the development of JexoPipe, a dedicated reduction and analysis pipeline, and JexoSim, a time-domain simulator for generating realistic observations and testing retrieval methodologies.

The Twinkle Cool Gas Giant Survey

I lead the Twinkle Cool Gas Giant Survey, a large-scale comparative survey of temperate giant exoplanets. The survey is designed to explore a largely unstudied population of planets that bridges the gap between hot Jupiters and the cold giant planets of our own Solar System. By measuring atmospheric composition, chemistry, and global trends across a statistically significant sample, the survey will establish the foundations of comparative studies of temperate giant exoplanets.

Hubble Space Telescope observations

My research has also included Hubble Space Telescope spectroscopy to investigate atmospheric variability and planetary evolution. Previous projects include studies of the hot Neptune LTT-9779 b and temporal changes in the atmosphere of the benchmark hot Jupiter HD 209458 b.

3. Developing the Next Generation of Exoplanet Observatories

In parallel with my observational research, I contribute to the design and scientific development of future exoplanet facilities. I have played a leading role in performance simulations, instrument modelling, and software development for ESA's Ariel mission, including the development of the original Ariel data reduction pipeline (ADaRP) and successive versions of the ExoSim simulator. I continue to contribute through leadership roles in Ariel's science and ground-segment working groups, including convening the Complementary Science Working Group.

Long-term vision

Over the next decade, I aim to combine JWST, Twinkle, Ariel, and future observatories to build a coherent understanding of planetary atmospheres across a wide range of environments. By linking atmospheric physics, comparative planetology, and astrobiology, my goal is to determine how planetary atmospheres evolve, how common habitable environments may be, and ultimately how observations can constrain the prevalence of life in the Universe.

Software developed

• ExoSim, SpotSim, ExoSim_N, JexoSim (JWST simulator), TwinkleSim, ADaRP, JexoPipe 

Teaching

Current undergraduate teaching

• PX4245 / PXT145 Exoplanets and the Search for Life: Module Organiser
• PX2140 Stars and Planets: Deputy Module Organiser
• Additionally I am DMO for Electromagnetism and Waves, and Astrophysics in Action 

Previous undergraduate teaching

• PX1127 Planet Earth: Module Organiser
• PX2140 Stars and Planets: guest lecturer
• PX1127 Planet Earth: Deputy Module Organiser
• PX2134 Structured Programming: Lab supervisor
• PX1125 Mathematical Practice for Physical Sciences: Marker
• PX1222 Mathematical Methods for Physicists 2: Marker

Other

• I supervise PhD, MPhys, MSc and BSc research projects (see supervision page)

Biography

Education

• PhD, Astrophysics, Cardiff University
• MSc (Distinction), Space Science, University College London
• Diploma in Physics (Distinction), Open University
• MA, Natural Sciences, Cambridge University
• MB, BChir, Medicine, Cambridge University
• Grad. Cert. Applied Sciences, Space Studies, University of South Australia
• Space Studies Program, International Space University

Professional memberships

• Fellow of the Royal Astronomical Society
• Fellow of the Higher Education Academy

Academic positions

• 2026-Present: Senior Lecturer, Cardiff University
• 2022-2026: Lecturer in Exoplanet Characterisation, School of Physics and Astronomy, Cardiff University
• 2017-2021: Post-doctoral Research Associate, Cardiff University
• 2013-2017: Post-graduate Research Student, Cardiff University
• 2003-2005: Visiting Researcher, Space Medicine & Health Care Systems Office, NASA Johnson Space Center, Houston.
• 2003-2005: Honorary Lecturer in Space Life Sciences, Dept. of Space & Climate Physics, University College London

Outreach and Media

• BBC Radio Wales Science Cafe interview about the ARIEL space mission (April 2018).
• Pythagorean Astronomy podcast interview about TESS, ARIEL and other exoplanet missions (April 2018).
• Exoplanet talks for Cardiff AS Level Summer Programmes 2018/19.
• Stargazing talk and telescope observing with Scouts (Spring 2019).
• Online astronomy talk with Scouts (Winter 2020).
• 'All About Space' magazine interview about Ariel mission ('Rise of the Exoplanet Hunter') (Jan 2021).
• Twinkle mission YouTube video ('The Founding Members') (Aug 2021).
• Pythagorean Astronomy podcast interview about JWST observing programme (Dec 2021).
• Cardiff School of Physics & Astronomy YouTube video about JWST (Dec 2021).
• BBC News Wales interview about exoplanets and JWST (July 2022).
• Nature News and Views article on JWST (Feb 2023).
• NASA/ESA Press release on JWST K2-18 b observation (Sep 2023)
• BBC News interview ('Alien life in the Universe') (Sep 2023)
• Le Parisien interview (Sep 2023)
• Hindustan Times interview (Sep 2023)
• News9Live (India) interview (Sep 2023)
• Kosmo magazine (Italy) interview (Oct 2023)
• IoP Festival of Physics, keynote speaker ('Exoplanets and the Search for Life') (Nov 2023)
• Astronomy on Tap (Cardiff) speaker (Nov 2023)
• Cardiff/Cambridge Press release on K2-18 b (April 2025)
• BBC News article on K2-18 b (April 2025)
• BBC Wales Radio interview (April 2025)
• RTE radio interview (April 2025)
• Sky News TV interview ("The News Hour with Mark Austin") (April 2025)
• The Standard podcast interview (April 2025)
• BBC Future interview "Exploring the peculiar smells of outer space" (May 2025)
• Scholastic "Science World" interview (June 2025)
• Sky News TV interview ("The World with Yalda Hakim") (Feb 2026)
• Cardiff University social media video about alien life (March 2026)

Committees and reviewing

• I am the post-graduate admissions tutor for the Astronomy Group. 
• I currently serve on the following school committees: a) Equality, diversity and inclusion (EDI), b) Environment and sustainability.
• I am on the CHART-GEI Schools Engagement Project management team and the Astronomy Instrumentation Group management team.
• I have previously served on the Ethics committee and MSc approval panel.
• JWST TAC exoplanet panel member for cycle 3 and cycle 4
• Grant reviewer for French National Research Agency and UKRI.
• I have refereed publications for journals including PASP, Nature and International Jourmal of Astrobiology.

Supervisions

Current supervision

• I am currently primary PhD supervisor for Megan Mealing. 
• My previous PhD student, Luke Booth, graduated in 2026.
• I am currently on the supervisory team as mentor for a number of PhD students.
• I currently supervise the undergraduate project "Exoplanet transmission spectroscopy"

Current supervision

Megan Mealing

Past projects

• Previous undergraduate and MSc projects include:  "Missions to the Planets", "Habitable exomoons", "Transmission spectroscopy of water", "Designing a telescope to observe Earth-like planet atmosphere", "Simulations for the Twinkle space mission", "Impact of star spots on exoplanet transmission spectroscopy"

News articles

Strongest hints yet of biological activity outside the solar system

17 April 2025

Chemical fingerprints of dimethyl sulfide and/or dimethyl disulfide observed in atmosphere of exoplanet K2-18b

Methane and carbon dioxide found in atmosphere of habitable zone exoplanet

25 September 2023

JWST advances search for habitable planets and life with observations of the sub-Neptune K2-18 b

Cardiff astronomers join Twinkle space mission

10 June 2021

Academics from the School of Physics and Astronomy are taking part in a pioneering space telescope project to understand more about planets beyond our Solar System