000006836 001__ 6836
000006836 005__ 20240217113350.0
000006836 0247_ $$2DOI$$a10.1089/ast.2018.1930
000006836 037__ $$aSCART-2024-0092
000006836 100__ $$aHakim, Kaustubh
000006836 245__ $$aMineralogy, Structure, and Habitability of Carbon-Enriched Rocky Exoplanets: A Laboratory Approach
000006836 260__ $$c2019
000006836 520__ $$aCarbon-enriched rocky exoplanets have been proposed to occur around dwarf stars as well as binary stars, white dwarfs, and pulsars. However, the mineralogical make up of such planets is poorly constrained. We performed high-pressure high-temperature laboratory experiments (P = 1–2 GPa, T = 1523–1823 K) on chemical mixtures representative of C-enriched rocky exoplanets based on calculations of protoplanetary disk compositions. These P-T conditions correspond to the deep interiors of Pluto- to Mars-sized planets and the upper mantles of larger planets. Our results show that these exoplanets, when fully differentiated, comprise a metallic core, a silicate mantle, and a graphite layer on top of the silicate mantle. Graphite is the dominant carbon-bearing phase at the conditions of our experiments with no traces of silicon carbide or carbonates. The silicate mineralogy comprises olivine, orthopyroxene, clinopyroxene, and spinel, which is similar to the mineralogy of the mantles of carbon-poor planets such as the Earth and largely unaffected by the amount of carbon. Metals are either two immiscible iron-rich alloys (S-rich and S-poor) or a single iron-rich alloy in the Fe-C-S system with immiscibility depending on the S/Fe ratio and core pressure. We show that, for our C-enriched compositions, the minimum carbon abundance needed for C-saturation is 0.05–0.7 wt% (molar C/O ∼0.002–0.03). Fully differentiated rocky exoplanets with C/O ratios more than that needed for C-saturation would contain graphite as an additional layer on top of the silicate mantle. For a thick enough graphite layer, diamonds would form at the bottom of this layer due to high pressures. We model the interior structure of Kepler-37b and show that a mere 10 wt% graphite layer would decrease its derived mass by 7%, which suggests that future space missions that determine both radius and mass of rocky exoplanets with insignificant gaseous envelopes could provide quantitative limits on their carbon content. Future observations of rocky exoplanets with graphite-rich surfaces would show low albedos due to the low reflectance of graphite. The absence of life-bearing elements other than carbon on the surface likely makes them uninhabitable.
000006836 594__ $$aNO
000006836 700__ $$aSpaargaren, Rob
000006836 700__ $$aGrewal, Damanveer S.
000006836 700__ $$aRohrbach, Arno
000006836 700__ $$aBerndt, Jasper
000006836 700__ $$aDominik, Carsten
000006836 700__ $$avan Westrenen, Wim
000006836 773__ $$n7$$pAstrobiology$$v19$$y2019
000006836 8560_ $$fkaustubh.hakim@ksb-orb.be
000006836 85642 $$ahttps://doi.org/10.1089/ast.2018.1930
000006836 8564_ $$s57165004$$uhttp://publi2-as.oma.be/record/6836/files/Hakim2019MineralogyCarbonExoplanets.pdf
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000006836 8564_ $$s3138$$uhttp://publi2-as.oma.be/record/6836/files/Hakim2019MineralogyCarbonExoplanets.gif?subformat=icon$$xicon
000006836 905__ $$apublished in
000006836 980__ $$aREFERD