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Title: Interior phase transformations and mass-radius relationships of silicon-carbon planets

Planets such as 55 Cancri e orbiting stars with a high carbon-to-oxygen ratio may consist primarily of silicon and carbon, with successive layers of carbon, silicon carbide, and iron. The behavior of silicon-carbon materials at the extreme pressures prevalent in planetary interiors, however, has not yet been sufficiently understood. In this work, we use simulations based on density functional theory to determine high-pressure phase transitions in the silicon-carbon system, including the prediction of new stable compounds with Si{sub 2}C and SiC{sub 2} stoichiometry at high pressures. We compute equations of state for these silicon-carbon compounds as a function of pressure, and hence derive interior structural models and mass-radius relationships for planets composed of silicon and carbon. Notably, we predict a substantially smaller radius for SiC planets than in previous models, and find that mass radius relationships for SiC planets are indistinguishable from those of silicate planets. We also compute a new equation of state for iron. We rederive interior models for 55 Cancri e and are able to place more stringent restrictions on its composition.
Authors:
 [1] ;  [2]
  1. CSIRO Materials Science and Engineering, Parkville, Victoria 3052 (Australia)
  2. Department of Earth and Planetary Science and Department of Astronomy, University of California, Berkeley, CA 94720 (United States)
Publication Date:
OSTI Identifier:
22365006
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 793; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON; DENSITY FUNCTIONAL METHOD; EQUATIONS OF STATE; FORECASTING; IRON; MASS; ORBITS; OXYGEN; PHASE TRANSFORMATIONS; PLANETS; PRESSURE DEPENDENCE; PRESSURE RANGE MEGA PA 10-100; SATELLITES; SILICATES; SILICON; SILICON CARBIDES; SIMULATION; STARS; STOICHIOMETRY