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Title: The role of carbon in extrasolar planetary geodynamics and habitability

The proportions of oxygen, carbon, and major rock-forming elements (e.g., Mg, Fe, Si) determine a planet's dominant mineralogy. Variation in a planet's mineralogy subsequently affects planetary mantle dynamics as well as any deep water or carbon cycle. Through thermodynamic models and high pressure diamond anvil cell experiments, we demonstrate that the oxidation potential of C is above that of Fe at all pressures and temperatures, indicative of 0.1-2 Earth-mass planets. This means that for a planet with (Mg+2Si+Fe+2C)/O > 1, excess C in the mantle will be in the form of diamond. We find that an increase in C, and thus diamond, concentration slows convection relative to a silicate-dominated planet, due to diamond's ∼3 order of magnitude increase in both viscosity and thermal conductivity. We assert then that in the C-(Mg+2Si+Fe)-O system, there is a compositional range in which a planet can be habitable. Planets outside of this range will be dynamically sluggish or stagnant, thus having limited carbon or water cycles leading to surface conditions inhospitable to life as we know it.
Authors:
; ; ;  [1] ;  [2]
  1. School of Earth Sciences, The Ohio State University, 125 South Oval Mall, Columbus, OH 43202 (United States)
  2. US Army Research Laboratory, RDRL-WML-B (Bldg. 390), Aberdeen Proving Ground, MD 21005 (United States)
Publication Date:
OSTI Identifier:
22370553
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 793; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; CARBON; CONCENTRATION RATIO; DIAMONDS; ELEMENT ABUNDANCE; IRON; MAGNESIUM; OXIDATION; OXYGEN; PLANETS; PRESSURE RANGE MEGA PA 10-100; SATELLITES; SILICON; STARS; SURFACES; THERMAL CONDUCTIVITY; THERMODYNAMIC MODEL; VARIATIONS; VISCOSITY; WATER