A New Wavelength Window into Escaping Exoplanet Atmospheres

Thursday 5 July, 10:40

Observational evidence of escaping exoplanet atmospheres has been obtained for a few exoplanets to date, mostly from strong transit signals in the ultraviolet, particularly the Lyman-alpha line. However, the Lyman-alpha line core is usually heavily affected by interstellar absorption and geocoronal emission, limiting the information that can be extracted from that part of the spectrum. Transit observations in atomic lines that are sensitive enough to trace the rarefied gas in the extended atmosphere, but do not suffer from significant absorption by the interstellar medium, could enable more detailed observations and thus provide better constraints on theoretical models of escaping atmospheres. The absorption line of helium at 10830 angstrom could satisfy both of these conditions. In this talk, I will present a new model of escaping planetary atmospheres used to predict in-transit absorption at 10830 A. Our results indicate that significant absorption at this wavelength can be expected in some exoplanets (Oklopcic & Hirata 2018). That prediction has recently been confirmed by Spake et al. (in press), who detected excess absorption at 10830 A in the transmission spectrum of WASP 107b. The helium 10830 A line is accessible for ground-based observations using high-resolution spectrographs, which could enable more detailed studies of extended atmospheres for a larger number of exoplanets than what is feasible with observations in the UV. By opening this new wavelength window into escaping atmospheres, we can improve our understanding of the physical processes that drive atmospheric escape and, consequently, affect planetary evolution and demographics of planetary systems.

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