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Title: Mass-Radius Relationships for Exoplanets

Journal Article · · The Astrophysical Journal
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [2];  [3]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Univ. Rostock (Germany)
  3. Univ. of Edinburgh (United Kingdom)

For planets other than Earth, particularly exoplanets, interpretation of the composition and structure depends largely on comparing the mass and radius with the composition expected given their distance from the parent star. The composition implies a mass–radius relation which relies heavily on equations of state calculated from electronic structure theory and measured experimentally on Earth. We lay out a method for deriving and testing equations of state, and deduce mass–radius and mass–pressure relations for key, relevant materials whose equation of state (EOS) is reasonably well established, and for differentiated Fe/rock. We find that variations in the EOS, such as may arise when extrapolating from low-pressure data, can have significant effects on predicted mass–radius relations and on planetary pressure profiles. The relations are compared with the observed masses and radii of planets and exoplanets, broadly supporting recent inferences about exoplanet structures. Kepler-10b is apparently "Earth-like," likely with a proportionately larger core than Earth's, nominally 2/3 of the mass of the planet. CoRoT-7b is consistent with a rocky mantle over an Fe-based core which is likely to be proportionately smaller than Earth's. GJ 1214b lies between the mass–radius curves for H2O and CH4, suggesting an "icy" composition with a relatively large core or a relatively large proportion of H2O. CoRoT-2b is less dense than the hydrogen relation, which could be explained by an anomalously high degree of heating or by higher than assumed atmospheric opacity. HAT-P-2b is slightly denser than the mass–radius relation for hydrogen, suggesting the presence of a significant amount of matter of higher atomic number. CoRoT-3b lies close to the hydrogen relation. The pressure at the center of Kepler-10b is 1.5+1.21.0 TPa. The central pressure in CoRoT-7b is probably close to 0.8 TPa, though may be up to 2 TPa. These pressures are accessible by planar shock and ramp-loading experiments at large laser facilities. Furthermore, the center of HAT-P-2b is probably around 210 TPa, in the range of planned National Ignition Facility experiments, and that of CoRoT-3b around 1900 TPa.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
1830946
Report Number(s):
LLNL-JRNL-421766; 383722; TRN: US2216560
Journal Information:
The Astrophysical Journal, Vol. 744, Issue 1; ISSN 0004-637X
Publisher:
IOP PublishingCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 103 works
Citation information provided by
Web of Science

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Cited By (32)

Ramp compression of diamond to five terapascals journal July 2014
The search for signs of life on exoplanets at the interface of chemistry and planetary science journal March 2015
Ion-beam-driven Planetary Physics Research at FAIR journal October 2018
Application of intense ion beams to planetary physics research at the Facility for Antiprotons and Ion Research facility journal January 2019
Electrical conductivity and magnetic dynamos in magma oceans of Super-Earths journal September 2018
Dynamical Ionic Clusters with Flowing Electron Bubbles from Warm to Hot Dense Iron along the Hugoniot Curve text January 2011
The PLATO 2.0 mission text January 2014
Threshold Radii of Volatile-rich Planets journal October 2018
Thermally driven Fermi glass states in warm dense matter: Effects on terahertz and direct-current conductivities journal September 2019
Experimental evidence for a phase transition in magnesium oxide at exoplanet pressures journal September 2013
Structure, equation of state, diffusion and viscosity of warm dense Fe under the conditions of giant planet core text January 2013
High-pressure chemistry of hydrocarbons relevant to planetary interiors and inertial confinement fusion journal May 2018
Beyond the exoplanet mass-radius relation journal October 2019
Atmosphere-Interior Exchange on Hot, Rocky Exoplanets journal September 2016
The exoplanet handbook: Book Review journal March 2012
Equation of state of iron under core conditions of large rocky exoplanets journal April 2018
Dynamic Ionic Clusters with Flowing Electron Bubbles from Warm to Hot Dense Iron along the Hugoniot Curve journal October 2012
WARM DUST AROUND COOL STARS: FIELD M DWARFS WITH WISE 12 OR 22 μm EXCESS EMISSION journal October 2014
Properties and Occurrence Rates for Kepler Exoplanet Candidates as a Function of Host Star Metallicity from the DR25 Catalog journal October 2018
Spinel and post-spinel phase assemblages in Zn2TiO4: an experimental and theoretical study journal September 2016
Laser-driven shock compression of “synthetic planetary mixtures” of water, ethanol, and ammonia journal July 2019
Quantum molecular dynamics study on the proton exchange, ionic structures, and transport properties of warm dense hydrogen-deuterium mixtures journal June 2018
Studies of equation of state properties of high-energy-density matter generated by intense ion beams at the facility for antiprotons and ion research journal February 2020
Threshold Radii of Volatile-rich Planets text January 2018
Multi-charge-state molecular dynamics and self-diffusion coefficient in the warm dense matter regime journal January 2018
Studies of the Core Conditions of the Earth and Super-Earths Using Intense Ion Beams at FAIR journal August 2017
Dynamic electron–ion collisions and nuclear quantum effects in quantum simulation of warm dense matter journal January 2018
Properties and occurrence rates of $Kepler$ exoplanet candidates as a function of host star metallicity from the DR25 catalog text January 2018
Warm Dust around Cool Stars: Field M Dwarfs with WISE 12 or 22 Micron Excess Emission text January 2014
Structure, equation of state, diffusion and viscosity of warm dense Fe under the conditions of a giant planet core journal April 2013
Ionization dynamics of dense matter generated by intense ultrashort X-ray pulses journal February 2019
From microjoules to megajoules and kilobars to gigabars: Probing matter at extreme states of deformation journal September 2015

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