Role of Magma Oceans in Controlling Carbon and Oxygen of Sub-Neptune Atmospheres
Most exoplanets with a few Earth radii are more inflated than bare-rock planets with the same mass, indicating a substantial volatile amount. Neither the origin of the volatiles nor the planet’s bulk composition can be constrained from the mass–radius relation alone, and the spectral characterizatio...
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2024-01-01
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| author | Chanoul Seo Yuichi Ito Yuka Fujii |
| author_facet | Chanoul Seo Yuichi Ito Yuka Fujii |
| author_sort | Chanoul Seo |
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| description | Most exoplanets with a few Earth radii are more inflated than bare-rock planets with the same mass, indicating a substantial volatile amount. Neither the origin of the volatiles nor the planet’s bulk composition can be constrained from the mass–radius relation alone, and the spectral characterization of their atmospheres is needed to solve this degeneracy. Previous studies showed that chemical interaction between accreted volatile and possible molten rocky surface (i.e., magma ocean) can greatly affect the atmospheric composition. However, a variety in the atmospheric compositions of such planets with different properties remains elusive. In this work, we examine the dependence of atmospheric H, O, and C on planetary parameters (atmospheric thickness, planetary mass, equilibrium temperature, and magma properties such as redox state) assuming nebula gas accretion on an Earth-like core, using an atmosphere-magma chemical equilibrium model. Consistent with previous work, we show that atmospheric H _2 O fraction on a fully molten rocky interior with an Earth-like redox state is on the order of 10 ^−2 –10 ^−1 regardless of other planetary parameters. Despite the solubility difference between H- and C-bearing species, C/H increases only a few times above the nebula value except for atmospheric pressure ≲1000 bar and H _2 O fraction ≳10%. This results in a negative O/H–C/O trend and depleted C/O below one-tenth of the nebula gas value under an oxidized atmosphere, which could provide a piece of evidence of rocky interior and endogenic water. We also highlight the importance of constraints on the high-pressure material properties for interpreting the magma–atmospheric interaction of inflated planets. |
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| language | English |
| publishDate | 2024-01-01 |
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| spelling | doaj-art-c9edafcb3aa24ac59af46b9ea4cb187a2025-08-20T02:09:26ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-0197511410.3847/1538-4357/ad7461Role of Magma Oceans in Controlling Carbon and Oxygen of Sub-Neptune AtmospheresChanoul Seo0https://orcid.org/0000-0002-0749-2090Yuichi Ito1https://orcid.org/0000-0002-0598-3021Yuka Fujii2https://orcid.org/0000-0002-2786-0786Department of Astronomical Science, School of Physical Sciences, Graduate University for Advanced Studies (SOKENDAI) , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan ; chanoul.seo@grad.nao.ac.jp; Division of Science, National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanDivision of Science, National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Faculty of Science and Technology, Sophia University , Kioi-Cho 7-1, Chiyoda-ku, Tokyo, 102-8554, Japan; Department of Physics and Astronomy, University College London , Gower Street, WC1E 6BT London, UKDepartment of Astronomical Science, School of Physical Sciences, Graduate University for Advanced Studies (SOKENDAI) , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan ; chanoul.seo@grad.nao.ac.jp; Division of Science, National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanMost exoplanets with a few Earth radii are more inflated than bare-rock planets with the same mass, indicating a substantial volatile amount. Neither the origin of the volatiles nor the planet’s bulk composition can be constrained from the mass–radius relation alone, and the spectral characterization of their atmospheres is needed to solve this degeneracy. Previous studies showed that chemical interaction between accreted volatile and possible molten rocky surface (i.e., magma ocean) can greatly affect the atmospheric composition. However, a variety in the atmospheric compositions of such planets with different properties remains elusive. In this work, we examine the dependence of atmospheric H, O, and C on planetary parameters (atmospheric thickness, planetary mass, equilibrium temperature, and magma properties such as redox state) assuming nebula gas accretion on an Earth-like core, using an atmosphere-magma chemical equilibrium model. Consistent with previous work, we show that atmospheric H _2 O fraction on a fully molten rocky interior with an Earth-like redox state is on the order of 10 ^−2 –10 ^−1 regardless of other planetary parameters. Despite the solubility difference between H- and C-bearing species, C/H increases only a few times above the nebula value except for atmospheric pressure ≲1000 bar and H _2 O fraction ≳10%. This results in a negative O/H–C/O trend and depleted C/O below one-tenth of the nebula gas value under an oxidized atmosphere, which could provide a piece of evidence of rocky interior and endogenic water. We also highlight the importance of constraints on the high-pressure material properties for interpreting the magma–atmospheric interaction of inflated planets.https://doi.org/10.3847/1538-4357/ad7461Exoplanet atmospheresExoplanet formationExtrasolar rocky planetsPlanetary interior |
| spellingShingle | Chanoul Seo Yuichi Ito Yuka Fujii Role of Magma Oceans in Controlling Carbon and Oxygen of Sub-Neptune Atmospheres The Astrophysical Journal Exoplanet atmospheres Exoplanet formation Extrasolar rocky planets Planetary interior |
| title | Role of Magma Oceans in Controlling Carbon and Oxygen of Sub-Neptune Atmospheres |
| title_full | Role of Magma Oceans in Controlling Carbon and Oxygen of Sub-Neptune Atmospheres |
| title_fullStr | Role of Magma Oceans in Controlling Carbon and Oxygen of Sub-Neptune Atmospheres |
| title_full_unstemmed | Role of Magma Oceans in Controlling Carbon and Oxygen of Sub-Neptune Atmospheres |
| title_short | Role of Magma Oceans in Controlling Carbon and Oxygen of Sub-Neptune Atmospheres |
| title_sort | role of magma oceans in controlling carbon and oxygen of sub neptune atmospheres |
| topic | Exoplanet atmospheres Exoplanet formation Extrasolar rocky planets Planetary interior |
| url | https://doi.org/10.3847/1538-4357/ad7461 |
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