Presentation #200.03 in the session “Exoplanets”.
Volatiles like H, C, and N appear to be concentrated in the atmospheres and hydrospheres of terrestrial planets, but a surprising fraction of these elements can be found locked in different phases throughout the planet’s crust and interior. Exchange of volatiles between these different reservoirs occurs throughout a planet’s evolution, from magma oceans during planet formation to deep volatile cycles throughout the planet’s geologic lifetime. Fluxes of volatiles into and out of the mantle play a key role in the stability of habitable conditions at the surface on geological timescales. The oxidation state of the mantle will affect both the speciation of volcanic gases and the magnitude of outgassing fluxes due to changes in volatile solubilities in silicate melts and possible stabilization of reduced phases (e.g. carbides, sulfides). To better understand the habitability of small planets, it is important to understand the coupled evolution of the surface and interior. In this talk, we will present estimates of plausible oxidation states of the mantles of Trappist-1d, e, and f derived from magma ocean evolution models, in combination with core and water mass fraction estimates from Agol et al. (2021). We then use a model of solid-state thermal evolution to quantify outgassing rates over the lifetime of the planets to the present-day. Coupled with a volatile evolution model, we derive outgassing rates of H and C gas species and weathering rates in both oxidized and reduced atmospheres. We will discuss implications for the evolution of climate of the Trappist-1 planets and other M dwarf planets. References: Agol et al. (2021) PSJ, doi:10.3847/PSJ/abd022. This work is supported by NASA under Grant No. 80NSSC21K0905 issued through the ICAR program.