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Atmospheric escape and near-UV signatures of ultra-hot Jupiters

Presentation #200.06 in the session Exoplanet Atmospheres: Giant Planets (Oral Presentation)

Published onOct 23, 2023
Atmospheric escape and near-UV signatures of ultra-hot Jupiters

Ultra-Hot Jupiters (UHJs) provide a natural laboratory of rapid atmospheric escape that can be used to test models of this process. UHJs have dayside temperatures in excess of 2200 K, which means that metals and heavy elements are not likely to condense on the dayside. Metals like Fe and Mg can often escape their atmospheres and are detectable in the near-UV. For example, the Ultra-Hot Jupiter WASP-121b is among the known transiting planets with the highest potential for atmospheric escape. This is confirmed by transmission spectra at different wavelengths, including in the NUV, that show evidence of the escape of hydrogen and metals from the planet’s atmosphere. A one-size-fits-all approach, however, does not apply to mass loss rates from UHJs. Many UHJs are relatively stable to mass loss by atmospheric escape, often because of their relatively high masses. We use detailed models of UHJ atmospheres, spanning from the lower atmosphere to the thermosphere, to demonstrate that the mass loss rate should depend much more strongly on planet mass than expected based on the standard energy-limited approach. We then discuss the NUV and other observations in the context of the results to further constrain the energy balance in UHJ atmospheres. In particular, we focus on NUV observations of WASP-121b and WASP-189b. While the NUV spectrum of WASP-121b was observed with the Hubble Space Telescope (HST), the NUV spectrum of WASP-189b was observed by the Colorado Ultraviolet Transit Experiment (CUTE) and it constitutes the first exoplanet transit spectrum observed with a small satellite.

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