Eclipse Mapping Exoplanet Atmospheres with the James Webb Space Telescope

Our understanding of exoplanets is significantly lacking in comparison to our understanding of the Solar System planets due to the greater difficulties of observing them. Many properties of exoplanets can be uncovered through the study of their atmospheres, which hold key information on their current state and formation history. The most successful exoplanet detection and characterisation method is the transit method, which allows us access to atmospheric information on the nightside hemisphere of an exoplanet whilst they are in transit and on the dayside hemisphere as they are eclipsed by their host star.

My research involves using the technique of eclipse mapping to spatially map the atmospheres of transiting exoplanets. If we take snapshot observations as progressive longitudes of the exoplanet enter eclipse, then we can attribute the reductions in system flux to that region of the planet and construct a 1D emission map of the dayside hemisphere of its atmosphere. If the orbit of the planet is inclined from our viewpoint, then higher latitudes will be eclipsed faster than lower latitudes, allowing us to further sub-attribute the flux reductions to different latitudes, extending our map to 2D. Observing the eclipse at multiple wavelengths then even further allows us to measure the emission from multiple depths of the atmosphere, extending the map to 3D.

Hot Jupiters (highly irradiated and tidally locked giant exoplanets with day-scale orbital periods) provide the most exemplary conditions for characterising the atmospheres of exoplanets, owing to their often highly inflated atmospheres which promote strong signals. My research focuses on eclipse mapping the dayside hemisphere of the hot Jupiter WASP-17b using Space Telescope GTO programme 1353 (PI: N.K. Lewis) data obtained by the MIRI/LRS and NIRSpec/G395H instruments onboard JWST. WASP-17b is a prime candidate for these types of observations as the day- to night-side temperature range of its atmosphere spans 1000 - 2500 K, making it likely to host a broad range of spectroscopically active chemical species. It is also an interesting target due to its retrograde orbit, which challenges current planet formation theories - my research aims to contribute to bridging gaps such as this in our understanding of planet formation.

This work is undertaken as part of the JWST-TST collaboration, with the aim of combining this dataset and others (three transits and three eclipses, one each respectively obtained by the MIRI/LRS, NIRSpec/G395H, and NIRISS/SOSS instrument onboard JWST, covering the 0.6 - 14 micron wavelength range) to produce the first full 3D map of an exoplanet atmosphere, which will allow us to robustly constrain its thermal, compositional, and dynamical properties, contributing momentously to our understanding of all aspects of exoplanet science. Such techniques will then be extended to other types of exoplanets in order to broaden our understanding of their diversity.