TRAPPIST-1

From CO2- to H2O-dominated Atmospheres And Back — How Mixed Outgassing Changes The Volatile Distribution In Magma Oceans Around M Dwarf Stars [TRAPPIST-1]

By Keith Cowing
Press Release
May 24, 2025
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From CO2- to H2O-dominated Atmospheres And Back — How Mixed Outgassing Changes The Volatile Distribution In Magma Oceans Around M Dwarf Stars [TRAPPIST-1]
This schematic depicts the set-up of the volatile exchange during initialization (t=0) and run time. For initialization, a surface temperature of 4000 K and a completely molten magma ocean is assumed, where the dissolved volatiles are in balance with the outgassed volatile content, set by the volatile melt fraction Fi . As the magma ocean solidifies, part of the volatile budget is deposited in the solid mantle. Further, atmospheric escape can remove H2O. These two sink terms thus reduce the amount of a volatile available in the fully coupled magma ocean-atmosphere system Mmoa i . The full overview of all included processes, including radiogenic heating, is shown in Barth et al. (2021, Fig. 1) — astro-ph.EP

We investigate the impact of CO2 on TRAPPIST-1 e, f and g during the magma ocean stage. These potentially habitable rocky planets are currently the most accessible for astronomical observations.

A constraint on the volatile budget during the magma ocean stage is a link to planet formation and also needed to judge their habitability. We perform simulations with 1-100 terrestrial oceans (TO) of H2O with and without CO2 and for albedos 0 and 0.75. The CO2 mass is scaled with initial H2O by a constant factor between 0.1 and 1.

The magma ocean state of rocky planets begins with a CO2-dominated atmosphere but can evolve into a H2O dominated state, depending on initial conditions. For less than 10 TO initial H2O, the atmosphere tends to desiccate and the evolution may end with a CO2 dominated atmosphere.

Otherwise, the final state is a thick (>1000 bar) H2O-CO2 atmosphere. Complete atmosphere desiccation with less than 10 TO initial H2O can be significantly delayed for TRAPPIST-1e and f, when H2O has to diffuse through a CO2 atmosphere to reach the upper atmosphere, where XUV photolysis occurs.

As a consequence of CO2 diffusion-limited water loss, the time of mantle solidification for TRAPPIST-1 e, f, and g can be significantly extended compared to a pure H2O evolution by up to 40 Myrs for albedo 0.75 and by up to 200 Mrys for albedo 0. The addition of CO2 further results in a higher water content in the melt during the magma ocean stage.

Our compositional model adjusted for the measured metallicity of TRAPPIST-1 yields for the dry inner planets (b, c, d) an iron fraction of 27 wt-%. For TRAPPIST-1 e, this iron fraction would be compatible with a (partly) desiccated evolution scenario and a CO2 atmosphere with surface pressures of a few 100 bar. A comparative study between TRAPPIST-1 e and the inner planets may yield the most insights about formation and evolution scenarios.

Ludmila Carone, Rory Barnes, Lena Noack, Katy L. Chubb, Patrick Barth, Bertram Bitsch, Alexander Thamm, Alexander Balduin, Rodolfo Garcia, Christiane Helling

Comments: 36 pages, 28 figues, accepted by A&A 9/12/2024
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2412.10192 [astro-ph.EP] (or arXiv:2412.10192v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2412.10192
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Journal reference: A&A 693, A303 (2025)
Related DOI:
https://doi.org/10.1051/0004-6361/202450307
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Submission history
From: Ludmila Carone
[v1] Fri, 13 Dec 2024 15:03:11 UTC (4,547 KB)
https://arxiv.org/abs/2412.10192

Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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