Oxidation of the Interiors of Carbide Exoplanets

Abstract

Astrophysical measurements have shown that some stars have sufficiently high carbon-to-oxygen ratios such that the planets they host would be mainly composed of carbides instead of silicates. We studied the behavior of silicon carbide in the presence of water under the high pressure-temperature conditions relevant to planetary interiors in the laser-heated diamond-anvil cell (LHDAC). When reacting with water, silicon carbide converts to silica (stishovite) and diamond at pressures up to 50 GPa and temperatures up to 2500 K: SiC + 2H${}_2$O -> SiO${}_2$ + C + 2H${}_2$. Therefore, if water can be incorporated into carbide planets during their formation or through later delivery, they could be oxidized and have mineralogy dominated by silicates and diamond in their interiors. The reaction could produce CH${}_4$ at shallower depths and H${}_2$ at greater depths which could be degassed from the interior, causing the atmospheres of the converted carbon planets to be rich in reducing gases. Excess water after the reaction can be stored in dense silica polymorphs in the interiors of the converted carbon planets. Such conversion of mineralogy to diamond and silicates would decrease the density of carbon-rich planet, making the converted planets distinct from silicate planets in mass-radius relations for the 2-8 Earth mass range.

arXiv comment11 pages, 5 figures

References in corpus (16)

• High C/O Ratio and Weak Thermal Inversion in the Very Hot Atmosphere of Exoplanet WASP-12b
• The Compositional Diversity of Extrasolar Terrestrial Planets: I. In-Situ Simulations
• Carbon-rich Giant Planets: Atmospheric Chemistry, Thermal Inversions, Spectra, and Formation conditions
• High-precision stellar abundances of the elements - methods and applications
• Spectroscopic Studies of the Vibrational and Electronic Properties of Solid Hydrogen to 285 GPa
• On the Carbon-to-Oxygen Ratio Measurement in Nearby Sunlike Stars: Implications for Planet Formation and the Determination of Stellar Abundances
• C/O Ratios of Stars with Transiting Hot Jupiter Exoplanets
• Carbon and Oxygen in Nearby Stars: Keys to Protoplanetary Disk Chemistry
• The carbon-to-oxygen ratio in stars with planets
• Carbon to oxygen ratios in extrasolar planetesimals
• The Role of Carbon in Extrasolar Planetary Geodynamics and Habitability
• C/O vs Mg/Si ratios in solar type stars: The HARPS sample
• Equation of state of SiC at extreme conditions: new insight into the interior of carbon rich exoplanets
• Mineralogy, structure and habitability of carbon-enriched rocky exoplanets: A laboratory approach
• High-resolution Spectroscopic Study of Dwarf Stars in the Northern Sky: Lithium, Carbon, and Oxygen Abundances
• Capturing the oxidation of silicon carbide in rocky exoplanetary interiors

Cited by in corpus (4)

• Eta-Earth Revisited II: Deriving a Maximum Number of Earth-like Habitats in the Galactic Disk
• Photosynthetic Fluorescence from Earth-Like Planets around Sun-Like and Cool Stars
• Proto-planetary disk composition-dependent element volatility in the context of rocky planet formation
• On the Need for a Classification System for Consistent Characterization of the Composition of Planetary Bodies