Internal Structure and CO$_2$ Reservoirs of Habitable Water-Worlds
Abstract
Water-worlds are water-rich (>1 wt% HO) 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% CO 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 CO-HO system, to explore the CO budget and to localize the main CO reservoirs inside of these planets. We show that CO dissolved in the ocean and trapped inside of a clathrate layer cannot accommodate a cometary amount of CO if the planet accretes more than 11 wt% of volatiles (CO + HO) during its formation. We propose a new, potentially dominant, CO reservoir for water-worlds: CO buried inside of the high-pressure water ice mantle as CO ices or (HCO . HO), monohydrate of carbonic acid. If insufficient amounts of CO 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.
Keywords
Cite
@article{arxiv.1904.10458,
title = {Internal Structure and CO$_2$ Reservoirs of Habitable Water-Worlds},
author = {Nadejda Marounina and Leslie A. Rogers},
journal= {arXiv preprint arXiv:1904.10458},
year = {2020}
}
Comments
Submitted to ApJ October 1st, 2018