Protoatmospheres and Surface Environment of Protoplanets |
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| Authors: | Yutaka Abe |
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| Institution: | (1) Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan |
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| Abstract: | Protoatmospheres and surface environment of terrestrial protoplanets during the oligarchic accretion phase and the giant impacts
phase are discussed from theoretical points of view. Mars-sized protoplanets form during the stage of the oligarchic growth.
Since protoplanets are formed from more or less ‘local’ planetesimals, the surface environment of the accreting protoplanets
depends on availability of volatile material in planetesimals. Even if no volatile-bearing planetesimals are available, a
gravitationary captured solar composition atmosphere is formed during accretion. In such cases the surface temperature is
always kept under the melting temperature of mantle silicate and only a subsurface magma ocean is formed. Core formation proceeds
under dry conditions, and volatile elements are not partitioned into metallic iron. Accretion of water-bearing planetesimals
results in impact degassing. A surface hydrous magma ocean forms in response to the thermal blanketing effect of the proto-atmosphere.
Then, some volatile materials dissolve into the magma ocean. If we consider reaction with metallic iron, the proto-atmosphere
is likely to be rich in hydrogen. In addition, a large amount of hydrogen may be partitioned into metallic iron under high
pressure, and delivered to the core. In the stage of giant impacts, both dry and water-bearing protoplanets collide on the
proto-Earth. Substantial amount of proto-atmosphere (including water vapor) survives giant impacts. Moreover, giant impacts
on protoplanets with oceans result in relative concentration of water against other gases. |
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