Internal Structure and CO2 Reservoirs of Habitable Water-Worlds

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Habitable Water-World

Water-worlds are water-rich (>1 wt% H2O) exoplanets. The classical models of water-worlds considered layered structures determined by the phase boundaries of pure water.

However, water-worlds are likely to possess comet-like compositions, with between ~3 mol% to 30 mol% CO2 relative to water. In this study, we build an interior structure model of habitable (i.e. surface-liquid-ocean-bearing) water-worlds using the latest results from experimental data on the CO2-H2O system, to explore the CO2 budget and to localize the main CO2 reservoirs inside of these planets.

We show that CO2 dissolved in the ocean and trapped inside of a clathrate layer cannot accommodate a cometary amount of CO2 if the planet accretes more than 11 wt% of volatiles (CO2 + H2O) during its formation. We propose a new, potentially dominant, CO2 reservoir for water-worlds: CO2 buried inside of the high-pressure water ice mantle as CO2 ices or (H2CO3 . H2O), monohydrate of carbonic acid. If insufficient amounts of CO2 are sequestered either in this reservoir or the planet's iron core, habitable zone water-worlds could generically be stalled in their cooling before liquid oceans have a chance to condense.

Nadejda Marounina, Leslie A. Rogers
(Submitted on 23 Apr 2019)
Comments: Submitted to ApJ October 1st, 2018
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1904.10458 [astro-ph.EP] (or arXiv:1904.10458v1 [astro-ph.EP] for this version)
Submission history
From: Nadejda Marounina
[v1] Tue, 23 Apr 2019 18:00:00 UTC (4,900 KB)
https://arxiv.org/abs/1904.10458
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