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Strong fractionation of deuterium and helium in sub-Neptune atmospheres along the radius valley

Presentation #625.05 in the session Planetary Atmospheres - Terrestrial Planets and Mini-Neptunes.

Published onApr 03, 2024
Strong fractionation of deuterium and helium in sub-Neptune atmospheres along the radius valley

We present novel results from IsoFATE, a new open-source numerical model that simulates atmospheric fractionation in escaping planetary atmospheres. We simulate the effects of EUV-driven photoevaporation and core-powered mass loss on deuterium-hydrogen and helium-hydrogen fractionation of sub-Neptune atmospheres around G, K, and M stars. Our model remains numerically stable at high fractionation rates, allowing us to explore a wider parameter space than has been possible previously. Our simulations predict a novel class of planets with super-Venus D/H ratios and helium-dominated atmospheres along the upper edge of the radius valley encompassing the habitable zone. Fractionation is mechanism-dependent, so constraining atmospheric He/H and D/H abundances offers a unique strategy to investigate the radius valley origin. Fractionation is also dependent on retained atmospheric mass, offering a proxy for planetary surface pressure and a way to distinguish between desiccated enveloped terrestrials and water worlds. Our data support a novel deuterium observing strategy in helium-dominated atmospheres. We present a list of promising targets for observational follow-up.

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