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Volatile acquisition from nebular atmospheres: a key to habitability of terrestrial planets

Friday March 8, 2019
3:30 pm

 Presenter:  Peter Olson, EPS UNM
 Series:  Physics and Astronomy Colloquium
 Abstract:  Discovery of thousands of exoplanets motivates the need to better understand the formation of habitable volatile-rich terrestrial planets. In collaboration with EPS Prof. Zachary Sharp, we are exploring volatile acquisition by nebular ingassing, in which an accreting planet absorbs volatiles from an atmosphere derived from its stellar nebula. Our approach combines gas transfer scaling laws obtained from ocean uptake of CO2 with a nebular atmosphere model, to calculate the amount of hydrogen and helium ingassed into terrestrial planets during their accretion.

For an Earth-sized (1 ME) body, we find that the surface pressure of its nebular atmosphere may exceed 0.5 kb and the surface temperature may approach 3000 K, turning the silicate crust and mantle into a super-heated, turbulent magma ocean. Under these conditions, Earth would have ingassed several ocean equivalents of hydrogen and orders of magnitude more primordial helium-3 than present-day mantle abundance. Later, as the nebular atmosphere dissipated, a portion of the hydrogen acquired during atmosphere growth degassed, raising the oxidation state of the silicate Earth to present-day conditions while leaving enough hydrogen in the mantle to produce the full inventory of surface water.

Because the pressure of a nebular atmosphere depends very strongly on the attracting mass, the planet mass accreted during the lifetime of its nebular atmosphere is a critical parameter for determining future habitability. We find that a Mars-sized (0.1 ME) terrestrial planet would acquire insignificant amounts hydrogen for water production from its nebular atmosphere, whereas a 4 ME body accreted in the same nebula would acquire 10s to 100s of ocean equivalents of hydrogen, leading to water-world conditions.
 Host:  Mousumi Roy
 Location:  Room 125, Dane Smith Hall

Refreshments will be available before the colloquium, at 03:15 pm, in in the lobby of Dane Smith Hall.

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