Institute of research into the fundamental laws of the Universe

"Observing the atmosphere of an exoplanet allows us to learn more about its formation and evolution, as well as the temperature, pressure and chemical conditions that prevail there. In the long term, these answers will enable us to characterize the exoplanets known to date, to understand the uniqueness of our solar system and assess the conditions of habitability", explains Achrène.

She began her doctoral research by developing a simulator capable of generating observations of exoplanetary atmospheres as the JWST would observe them through its Low-Resolution Spectrometer (LRS) of the MIRI instrument. This step is crucial for understanding and mitigating all the instrument's systematics that could bias the results. With this experience, she contributed to characterizing the in-flight performance of the first images acquired by the MIRI instrument and tested analysis methods using these simulated observations.

After this testing phase known as Early Release Science (ERS), the James Webb began making observations of exoplanets, and Achrène followed suit. She collaborated with various international teams, using her knowledge of the instrument and her simulator to analyze the atmospheres of other worlds. Many major discoveries followed, some of which were published in the prestigious journal Nature. These include, for example, the first detection of thermal emission from a temperate rocky planet; or the discovery of carbon dioxide in the atmosphere of a hot Jupiter (very close to its star) and sulfur dioxide in the atmosphere of two giants gas, the first evidence of photochemistry in the atmosphere of an exoplanet. Or the analysis of the phase curve (variation in the apparent luminous intensity of a planet along its orbit) of a Mini-Neptune.