Chloe Fisher

Postdoc at the University of Bern
working on Exoplanet Atmospheres.

Recent Projects

Predicted vs real values for CCF retrievals

Retrievals of High-Resolution Data

We have developed a technique to perform atmospheric retrieval on ground-based high-resolution data of exoplanets, involving cross-correlation functions and our previously developed random forest analysis. We applied our method to the ultra-hot jupiter KELT-9b.

Non-LTE vs LTE Sodium doublet

Non-LTE Analysis of Sodium

We investigated the effects of dropping the LTE assumption for sodium on high- and low-res data, and explored the differences in the atmospheric retrieval results.

H2O abundance vs Mass retrieval results

Retrieval Analysis of WFC3 Data

We studied a population of planets with WFC3 data to look for trends in their properties and investigate issues with the current techniques used to examine transmission spectra.


I am working on developing atmospheric retrieval methods involving machine learning techniques for extrasolar planets. I also work on different aspects of the theory of transimission spectra, and analysing traditional methods of retrieval.

Chloe giving an outreach talk at Pint of Science Bern 2019

First Author Papers

Fisher, C., et al. 2020, AJ, 159, 192
Interpreting High-Resolution Spectroscopy of Exoplanets Using Cross-Correlations and Supervised Machine Learning

Fisher, C., & Heng, K. 2019, ApJ, 881, 25
How much information does the sodium doublet encode? Retrieval analysis of Non-LTE sodium lines at low and high spectral resolutions

Fisher, C., & Heng, K. 2018, MNRAS, 481, 4698
Retrieval analysis of 38 WFC3 transmission spectra and resolution of the normalization degeneracy

Other Papers

Grimm, S. L., et al. 2021, ApJS, 253, 30
HELIOS-K 2.0 Opacity Calculator and Open-source Opacity Database for Exoplanetary Atmospheres

Guzmán Mesa, A., et al. 2020, AJ, 160, 15
Information content of JWST-NIRSPEC transmission spectra of warm Neptunes

Oreshenko, M., et al. 2020, AJ, 159, 6
Supervised Machine Learning for Intercomparison of Model Grids of Brown Dwarfs: Application to GJ 570D and the Epsilon Indi B Binary System

Hoeijmakers, H. J., et al. 2019, A&A, 627, A165
A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9b

Seidel, J. V., et al. 2019, A&A, 623, A166
Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) - II. A broadened sodium feature on the ultra-hot giant WASP-76b

Márquez-Neila, P., Fisher, C., Sznitman, R., & Heng, K. 2018, Nature Astronomy, 2, 719
Supervised machine learning for analysing spectra of exoplanetary atmospheres


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Our random forest retrieval code HELA, along with all the Exoclimes Simulation Platform open-source codes, can be found on our github page.

About Me

I am a postdoc at the University of Bern in Switzerland. I am working in Professor Kevin Heng's group at the Centre for Space and Habitability. We study the atmospheres of extrasolar planets to try to determine their composition and climate. Born in the UK, I did my undergraduate degree in mathematics at the University of Cambridge, followed by a master's in Astrophysics. In August, 2017 I joined Kevin's group in Bern, and in September 2021 I completed my PhD.

Chloe skiing in the Adelboden/Lenk region

Tweet from University of Bern International Relations department. Below is a screen shot of the video showing Chloe's face.

The University of Bern International Relations department have made a short video about my research and what life in Bern is like for international students. Click below to watch it.


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University of Bern
Centre for Space and Habitability (CSH)

Gesellschaftsstrasse 6 (G6)
3012 Bern