Dr Ryan MacDonald
Lecturer in Extrasolar Planets
Biography
Dr Ryan MacDonald is an expert in the atmospheres of planets orbiting other stars (exoplanets). He joined the School in 2025, after completing a NASA Sagan Fellowship at the University of Michigan and serving as a Research Associate at Cornell University's Carl Sagan Institute. Dr MacDonald completed his PhD in 2019 at the University of Cambridge, where he developed new Bayesian techniques to characterise exoplanet atmospheres.
Research areas
Exoplanet science raises some of the most profound questions in modern astronomy. What is the nature of worlds around other stars? Do the rocky planets in our galaxy resemble Earth, or is our blue marble an anomaly? Are we alone in the Universe?
Dr MacDonald's research at St Andrews combines cutting-edge telescope observations—such as the James Webb Space Telescope—with state-of-the-art theoretical modelling to decode exoplanet atmospheres. He is the lead developer of the POSEIDON atmospheric retrieval code, which has enabled numerous breakthroughs in exoplanet science, including:
- The first detection of titanium oxide in an exoplanet atmosphere (Sedaghati et al. 2017)—ESO press release.
- The first detection of mineral clouds in a transiting exoplanet atmospheres (Grant et al., 2023)—NASA press release.
- The first discovery of a 'steam world' (Piaulet-Ghorayeb et al., 2024)—University of Michigan press release.
Dr MacDonald leads several observing programs using JWST to characterise exoplanet atmospheres, whilst also being a core member of many international collaborations with access to ground- and space-based exoplanet spectra.
Students at St Andrews working with Dr MacDonald will therefore be directly involved with research at the frontier of exoplanetary science.
PhD supervision
- Sten Vermeiren
Selected publications
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Open access
TRIDENT: a rapid 3D radiative-transfer model for exoplanet transmission spectra
MacDonald, R. J. & Lewis, N. K., 10 Apr 2022, In: The Astrophysical Journal. 929, 1, 32 p., 20.Research output: Contribution to journal › Article › peer-review
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Open access
The White Dwarf Opportunity: Robust Detections of Molecules in Earth-like Exoplanet Atmospheres with the James Webb Space Telescope
Kaltenegger, L., MacDonald, R. J., Kozakis, T., Lewis, N. K., Mamajek, E. E., McDowell, J. C. & Vanderburg, A., 20 Sept 2020, In: The Astrophysical Journal Letters. 901, 1, 9 p., L1.Research output: Contribution to journal › Article › peer-review
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Open access
JWST-TST DREAMS: quartz clouds in the atmosphere of WASP-17b
Grant, D., Lewis, N. K., Wakeford, H. R., Batalha, N. E., Glidden, A., Goyal, J., Mullens, E., MacDonald, R. J., May, E. M., Seager, S., Stevenson, K. B., Valenti, J. A., Visscher, C., Alderson, L., Allen, N. H., Cañas, C. I., Colón, K., Clampin, M., Espinoza, N. & Gressier, A. & 22 others, , 20 Oct 2023, In: Astrophysical Journal Letters. 956, 2, 15 p., L32.Research output: Contribution to journal › Letter › peer-review
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Detection of titanium oxide in the atmosphere of a hot Jupiter
Sedaghati, E., Boffin, H. M. J., MacDonald, R. J., Gandhi, S., Madhusudhan, N., Gibson, N. P., Oshagh, M., Claret, A. & Rauer, H., 14 Sept 2017, In: Nature. 549, p. 238-241 18 p.Research output: Contribution to journal › Article › peer-review
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Open access
Double trouble: two transits of the super-Earth GJ 1132 b observed with JWST NIRSpec G395H
May, E. M., MacDonald, R. J., Bennett, K. A., Moran, S. E., Wakeford, H. R., Peacock, S., Lustig-Yaeger, J., Highland, A. N., Stevenson, K. B., Sing, D. K., Mayorga, L. C., Batalha, N. E., Kirk, J., Lopez-Morales, M., Valenti, J. A., Alam, M. K., Alderson, L., Fu, G., Gonzalez-Quiles, J. & Lothringer, J. D. & 2 others, , 11 Dec 2023, In: Astrophysical Journal Letters. 959, 1, 17 p., L9.Research output: Contribution to journal › Letter › peer-review
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Open access
HD 209458b in new light: evidence of nitrogen chemistry, patchy clouds and sub-solar water
MacDonald, R. J. & Madhusudhan, N., 24 May 2017, In: Monthly Notices of the Royal Astronomical Society. 469, 2, p. 1979-1996 18 p.Research output: Contribution to journal › Article › peer-review
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Open access
POSEIDON: a multidimensional atmospheric retrieval code for exoplanet spectra
MacDonald, R. J., 13 Jan 2023, In: Journal of Open Source Software. 8, 81, 6 p., 4873.Research output: Contribution to journal › Article › peer-review