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Survival of Primordial Planetary Atmospheres: Mass Loss from Hot and Temperate Low-Mass Planets

Presentation #1120 in the session “Open Engagement Session B”.

Published onMar 17, 2021
Survival of Primordial Planetary Atmospheres: Mass Loss from Hot and Temperate Low-Mass Planets

The most widely-studied mechanism of mass loss from extrasolar planets is photoevaporation via XUV ionization, primarily in the context of highly irradiated planets. However, the EUV dissociation of hydrogen molecules can also theoretically drive atmospheric evaporation on low-mass planets. For temperate planets such as the early Earth, impact erosion is expected to dominate in the traditional planetesimal accretion model, but it would be greatly reduced in pebble accretion scenarios, allowing other mass loss processes to be major contributors. We apply the same prescription for photoionization to this photodissociation mechanism and compare it to other possible sources of mass loss for temperate “early Earth”-type planets and highly irradiated “mini-Neptune”-type planets to retrieve the observed “evaporation valley.” We find that photodissociation is likely a subdominant, but significant component of mass loss for many of these planets. This mechanism could also preferentially remove hydrogen from a planet’s primordial atmosphere, thereby leaving a larger abundance of primordial water. We discuss the implications of these results for models of the formation and evolution of rocky planets.


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