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Lisa Dang. Credit: Ashutosh Gupta. Lisa Dang, an iREx student at McGill University, submitted her thesis in summer 2022. Here she summarizes the research projects she carried out as part of her Ph.D. Studying the climates of distant exoplanets with the Spitzer Space Telescope During my PhD, I used data from NASA’s Spitzer Space Telescope to study exoplanets. Spitzer, a telescope that operated between 2003 and 2020, was not specifically designed to study exoplanets. However, because it operates in the infrared region, where the planets are brightest, this telescope has helped us learn more about these new worlds and achieve several firsts in our field. Thanks to Spitzer, astronomers were able for the first time to observe an exoplanet throughout its course around its star and obtain what is called a phase curve. This phase curve, which shows the brightness of the planet as different parts of its surface are exposed, enables us to infer the presence of an atmosphere and to study how the temperature varies with longitude. During my studies, I was able to learn more about the climate of many exoplanets by studying their phase curves. The first, CoRoT-2b, is a young hot Jupiter that has a circular orbit, meaning its distance from its star is roughly constant. The second, XO-3b, is a massive hot Jupiter that has an eccentric orbit, its distance from its star thus varying significantly. The third, 55 Cancri e, is a rocky planet very close to its star, so its surface is probably covered in lava. Artist’s rendering of the exoplanet 55 Cancri e, studied by Lisa Dang during her dissertation. Credit: ESA/Hubble. Studying the phase curves I obtained for CoRoT-2b, XO-3b and 55 Cancri e, I realized that the climate of an exoplanet near its star cannot be explained only by its current position around the star. What’s interesting about this result is that our observations could potentially tell us more about the history of these hot worlds. Furthermore, I realized that it is not easy to infer the physical characteristics of exoplanets from their phase curves. It is necessary to obtain other observations to know precisely the brightness of the planet at different wavelengths and thus to eliminate the effects related to the instruments. During my thesis, I also had the opportunity to explore another technique for detecting and studying exoplanets, the gravitational lensing method. In fact, the same space telescope, Spitzer, has also been used to study exoplanets far away from their star, beyond the so-called ice line, using this method. In short, my thesis demonstrates how Spitzer paved the way for the study of exoplanets with the new generation instruments and observatories that have come or are now coming online, especially those dedicated to exoplanets. More information Lisa completed her PhD at McGill University between 2018 and 2022 under the supervision of Nicolas Cowan of McGill University. Her thesis will be available soon.

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