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The extreme physical properties of the CoRoT-7b super-Earth |
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| Authors: | A. Lé ger,O. Grasset,F. Codron,P. Barge,P. Cance,F. Catalano,O. Demangeon,S. Ferraz-Mello,J.-M. Grieß meier,G. Libourel,S.N. Raymond,D. Rouan,L. Schaefer,P.A. Schuller,F. Selsis,C. Sotin |
| Affiliation: | a Institut d’Astrophysique Spatiale, Université Paris-Sud, bât 121, Univ. Paris-Sud, F-91405 Orsay, France b Institut d’Astrophysique Spatiale, CNRS (UMR 8617), bât 121, Univ. Paris-Sud, F-91405 Orsay, France c Université de Nantes, CNRS, Lab de planétologie et Géodynamique, UMR-CNRS 6112, F-44300 Nantes, France d Planetary Chemistry Laboratory McDonnell Center for the Space Sciences, Dep. of Earth and Planetary Sciences, Washington University in St. Louis, USA e Laboratoire de Météorologie Dynamique, Université Pierre et Marie Curie-Paris 6, CNRS, Paris, France f Ecole Normale Supérieure (LST), 69364 Lyon Cedex 7, France g Laboratoire d’Astrophysique de Marseille, Pôle de l’Étoile, 38 r. Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France h Department of Astronomy, University of Washington, Seattle, WA 98195-1580, USA i 12 av. Fontaine de la Reine, 92430 Marnes la Coquette, France j IAG-Universidade de Sao Paulo, Rua do Matão, 1226, CEP05508-900-São Paulo, Brazil k CRPG-CNRS, 15 r. Notre-Dame des Pauvres, BP 20, 54501 Vandoeuvre les Nancy, France l Université de Bordeaux, Observatoire Aquitain des Sciences de l’Univers, 2 r. de l’Observatoire, BP 89, F-33271 Floirac Cedex, France m LESIA, UMR 8109 CNRS, Observatoire de Paris, UVSQ, Université Paris-Diderot, 5 pl. J. Janssen, 92195 Meudon, France n LUTH, UMR 8102 CNRS, Observatoire de Paris-Meudon, 5 pl. J. Janssen, 92195 Meudon, France o Jet Propulsion Laboratory, California Technology Institute, Pasadena, CA, USA p National Solar Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719-4933, USA q CNRS, UMR 5804, Lab. d’Astrophysique de Bordeaux, 2 r. de l’Observatoire, BP 89, F-33271 Floirac Cedex, France r Lab. de Physique et Chimie de l’Environnement et de l’Espace (LPC2E) & Obs. des Sciences de l’Univers en région Centre (OSUC), Orléans |
| Abstract: | The search for rocky exoplanets plays an important role in our quest for extra-terrestrial life. Here, we discuss the extreme physical properties possible for the first characterised rocky super-Earth, CoRoT-7b (Rpl = 1.58 ± 0.10 REarth, Mpl = 6.9 ± 1.2 MEarth). It is extremely close to its star (a = 0.0171 AU = 4.48 Rst), with its spin and orbital rotation likely synchronised. The comparison of its location in the (Mpl, Rpl) plane with the predictions of planetary models for different compositions points to an Earth-like composition, even if the error bars of the measured quantities and the partial degeneracy of the models prevent a definitive conclusion. The proximity to its star provides an additional constraint on the model. It implies a high extreme-UV flux and particle wind, and the corresponding efficient erosion of the planetary atmosphere especially for volatile species including water. Consequently, we make the working hypothesis that the planet is rocky with no volatiles in its atmosphere, and derive the physical properties that result. As a consequence, the atmosphere is made of rocky vapours with a very low pressure (P ? 1.5 Pa), no cloud can be sustained, and no thermalisation of the planet is expected. The dayside is very hot (2474 ± 71 K at the sub-stellar point) while the nightside is very cold (50-75 K). The sub-stellar point is as hot as the tungsten filament of an incandescent bulb, resulting in the melting and distillation of silicate rocks and the formation of a lava ocean. These possible features of CoRoT-7b could be common to many small and hot planets, including the recently discovered Kepler-10b. They define a new class of objects that we propose to name “Lava-ocean planets”. |
| Keywords: | Extrasolar planets Terrestrial planets Exobiology |
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