Thermal evolution of rocky exoplanets with a graphite outer shell

Abstract

The presence of rocky exoplanets with a large refractory carbon inventory is predicted by chemical evolution models of protoplanetary disks of stars with photospheric C/O >0.65, and by models studying the radial transport of refractory carbon. High-pressure high-temperature laboratory experiments show that most of the carbon in these exoplanets differentiates into a graphite outer shell. Our aim is to evaluate the effects of a graphite outer shell on the thermal evolution of rocky exoplanets containing a metallic core and a silicate mantle. We implement a parameterized model of mantle convection to determine the thermal evolution of rocky exoplanets with graphite layer thicknesses up to 1000 km. We find that, due to the high thermal conductivity of graphite, conduction is the dominant heat transport mechanism in a graphite layer for the long-term evolution (>200 Myr). The conductive graphite shell essentially behaves like a stagnant lid with a fixed thickness. Models of Kepler-37b (Mercury-size) and a Mars-sized exoplanet show that a planet with a graphite lid cools faster than a planet with a silicate lid, and a planet without a stagnant lid cools the fastest. A graphite lid needs to be approximately ten times thicker than a corresponding silicate lid in order to produce similar thermal evolution.

13 pages, 6 figures

References in corpus (21)

• Mass-Radius Relationships for Solid Exoplanets
• Internal Structure of Massive Terrestrial Planets
• Accurate, Empirical Radii and Masses of Planets and their Host Stars with Gaia Parallaxes
• The California-Kepler Survey. IV. Metal-rich Stars Host a Greater Diversity of Planets
• Spectral Properties of Cool Stars: Extended Abundance Analysis of 1617 Planet Search Stars
• The Compositional Diversity of Extrasolar Terrestrial Planets: I. In-Situ Simulations
• Inevitability of Plate Tectonics on Super-Earths
• A sub-Mercury-sized exoplanet
• Chemical Clues on the Formation of Planetary Systems: C/O vs Mg/Si for HARPS GTO Sample
• A new ab initio equation of state of hcp-Fe and its implication on the interior structure and mass-radius relations of rocky super-Earths
• A new class of Super-Earths formed from high-temperature condensates: HD219134 b, 55 Cnc e, WASP-47 e
• Chemistry in an Evolving Protoplanetary Disk: Effects on Terrestrial Planet Composition
• Carbon and Oxygen in Nearby Stars: Keys to Protoplanetary Disk Chemistry
• Beyond the Iron Peak: r- and s-process Elemental Abundances in Stars with Planets
• The Compositional Diversity of Extrasolar Terrestrial Planets: II. Migration Simulations
• The Role of Carbon in Extrasolar Planetary Geodynamics and Habitability
• Radial and vertical dust transport inhibit refractory carbon depletion in protoplanetary disks
• Carbon cycling and interior evolution of water-covered plate tectonics and stagnant lid planets
• Mineralogy, structure and habitability of carbon-enriched rocky exoplanets: A laboratory approach
• Capturing the oxidation of silicon carbide in rocky exoplanetary interiors
• Carbon-to-Oxygen Ratios in M dwarfs and Solar-type stars

Cited by in corpus (5)

• Atmospheres of Rocky Exoplanets
• Super-Earths and Earth-like Exoplanets
• Interior Controls on the Habitability of Rocky Planets
• Eta-Earth Revisited II: Deriving a Maximum Number of Earth-like Habitats in the Galactic Disk
• Sensitivity of Dry Lava Planet Atmospheric Emission Spectra to Changes in Lava Compositions