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Rocky super-Earth interiors - Structure and internal dynamics of CoRoT-7b and Kepler-10b

Wagner, F.W. and Tosi, N. and Sohl, F. and Rauer, H. and Spohn, T. (2012) Rocky super-Earth interiors - Structure and internal dynamics of CoRoT-7b and Kepler-10b. Astronomy and Astrophysics, 541 (A103), pp. 1-13. DOI: 10.1051/0004-6361/201118441.

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Official URL: http://dx.doi.org/10.1051/0004-6361/201118441

Abstract

Aims. We present interior structure models of the recently discovered exoplanets CoRoT-7b and Kepler-10b addressing their bulk compositions, present thermal states, and internal dynamics. We investigate how mantle convection patterns are influenced by the depth-dependence of thermodynamic parameters (e.g., thermal expansivity and conductivity) caused by the extended pressure and temperature ranges within rocky super-Earths. Methods. To model the interior of rocky exoplanets, we construct a four-layer structural model solving the mass and energy balance equations in conjunction with a generalized Rydberg equation of state providing the radial density distribution within each layer. The present thermal state is calculated according to a modified mixing-length approach for highly viscous fluids. Furthermore, the obtained internal structure is used to carry out two-dimensional convection simulations to visualize the mantle convection pattern within massive exoplanets such as CoRoT-7b and Kepler-10b. Results. Both CoRoT-7b and Kepler-10b most likely have large iron cores and a bulk composition similar to that of Mercury. For a planetary radius of Rp = (1.58 �± 0.10) Râ��, a revised total mass of Mp = (7.42 �± 1.21) Mâ��, and the existence of a third planet in the CoRoT-7 planetary system, calculations suggest that an iron core of 64 wt-% and a silicate mantle of 36 wt-% is produced owing to the relatively high average compressed density of ��avg = (10.4 �± 1.8) g cm-3. Kepler-10bâ��s planetary radius and total mass yield an iron core of 59.5 wt-%, which complements the silicate mantle of 40.5 wt-%. An enhanced radiogenic heating rate owing to CoRoT-7bâ��s young age (1.2â��2.3 Gyr) raises the radial distribution of temperature by only a few hundred Kelvin, but reduces the viscosity by an order of magnitude. The planform of mantle convection is found to be strongly modified for depth-dependent material properties, with hot plumes rising across the whole mantle and cold slabs, which stagnate in the mid-mantle because of the loss of buoyancy. Conclusions. We use a new model approach to determine the detailed interior structures and present thermal states of CoRoT-7b and Kepler-10b. Both planets are found to be enriched in iron. The results imply that modest radiogenic heating does not play a significant role in determining the internal structure of rocky exoplanets. The depth-dependence of thermodynamic properties, however, strongly influences the mantle convection patterns within exoplanets such as CoRoT-7b and Kepler-10b. This may have a significant effect on the thermal evolution and magnetic field generation of close-in super-Earths.

Document Type:Article
Title:Rocky super-Earth interiors - Structure and internal dynamics of CoRoT-7b and Kepler-10b
Authors:
AuthorsInstitution or Email of Authors
Wagner, F.W.frank.wagner@dlr.de
Tosi, N.nicola.tosi@dlr.de
Sohl, F.frank.sohl@dlr.de
Rauer, H.heike.rauer@dlr.de
Spohn, T.tilman.spohn@dlr.de
Date:10 May 2012
Journal or Publication Title:Astronomy and Astrophysics
Refereed publication:Yes
In Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:541
DOI:10.1051/0004-6361/201118441
Page Range:pp. 1-13
Status:Published
Keywords:planets and satellites: interiors / planets and satellites: composition / planets and satellites: individual: CoRoT-7b / planets and satellites: individual: Kepler-10b
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EW - Erforschung des Weltraums
DLR - Research area:Space
DLR - Program:W EW - Erforschung des Weltraums
DLR - Research theme (Project):W - Projekt COROT Beteiligung (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Physics
Institute of Planetary Research > Extrasolar Planets and Atmospheres
Deposited By: Frank Sohl
Deposited On:30 May 2012 08:24
Last Modified:12 Dec 2013 21:34

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