The Abundance of Atmospheric CO{sub 2} in Ocean Exoplanets: a Novel CO{sub 2} Deposition Mechanism

Journal Article · Mon Mar 20 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA5CFE· OSTI ID:22661254

Levi, A.; Sasselov, D. ^[1]

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1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

We consider super-Earth sized planets which have a water mass fraction large enough to form an external mantle composed of high-pressure water-ice polymorphs and also lack a substantial H/He atmosphere. We consider such planets in their habitable zone, so that their outermost condensed mantle is a global, deep, liquid ocean. For these ocean planets, we investigate potential internal reservoirs of CO{sub 2}, the amount of CO{sub 2} dissolved in the ocean for the various saturation conditions encountered, and the ocean-atmosphere exchange flux of CO{sub 2}. We find that, in a steady state, the abundance of CO{sub 2} in the atmosphere has two possible states. When wind-driven circulation is the dominant CO{sub 2} exchange mechanism, an atmosphere of tens of bars of CO{sub 2} results, where the exact value depends on the subtropical ocean surface temperature and the deep ocean temperature. When sea-ice formation, acting on these planets as a CO{sub 2} deposition mechanism, is the dominant exchange mechanism, an atmosphere of a few bars of CO{sub 2} is established. The exact value depends on the subpolar surface temperature. Our results suggest the possibility of a negative feedback mechanism, unique to water planets, where a reduction in the subpolar temperature drives more CO{sub 2} into the atmosphere to increase the greenhouse effect.

• OSTI ID: 22661254
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 838; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
CARBON DIOXIDE
DEPOSITION
FEEDBACK
GREENHOUSE EFFECT
ICE
LIQUIDS
MASS
PLANETS
REDUCTION
SATELLITE ATMOSPHERES
SATELLITES
SATURATION
SEAS
STEADY-STATE CONDITIONS
SURFACES
WATER