A SpectroPhotometric Inquiry of Close-in Exoplanets around the Desert to Understand their Nature and Evolution

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Half of known exoplanets orbit close to their star, featuring a desert of hot Neptunes whose origins remain uncertain. These planets may have lost their gas atmosphere, eroding into the dust-rich rocky planets found below the desert. Testing this scenario requires deriving accurate mass losses, but a lack of observational tracers prevented us from validating and refining models of escaping atmospheres. The coupling of atmospheric evolution with orbital migration, which can bring planets close to their star in various ways and delay their erosion, also remains to be explored. My work on infrared spectroscopy recently opened a new window into atmospheric escape, complementing traditional ultraviolet observations. I further brought to light an interplay between escape and migration by discovering that two warm Neptunes survive on the edge of the desert despite strong mass loss. I showed from one of these planets' orbital architecture that it migrated recently, triggering its erosion. These breakthroughs highlight the way to determine the origin of the desert: 1) Gathering UV/IR spectra (gas) and Vis/IR photometry (dust) for a representative sample of planets around the desert 2) Developing a self-consistent model of escaping atmosphere, validated by observations, which accounts for dust and gas physics. Interpreting data from 1) with this cutting-edge model will yield accurate mass loss for both gaseous and rocky planets 3) Measuring the sample orbital architectures, and combining them with mass losses for the first time to constrain population syntheses coupling long-term orbital and atmospheric evolution. This ambitious approach, exploiting advanced modeling informed by the most relevant tracers, will unveil the evolutionary tracks of exoplanets and bring insights into their nature. Challenges lie in developing a versatile atmospheric model and acquiring a sufficient sample. We will build upon existing codes, and exploit surveys led by the PI and his collaborators