Volume 531, July 2011
|Number of page(s)||11|
|Section||Planets and planetary systems|
|Published online||30 May 2011|
The multiple planets transiting Kepler-9
I. Inferring stellar properties and planetary compositions⋆
Université de Nice-Sophia Antipolis, CNRS UMR 6202, Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, France
2 Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Ave, Cambridge, MA, 02139, USA
Received: 25 February 2011
Accepted: 30 March 2011
The discovery of multiple transiting planetary systems offers new possibilities for characterising exoplanets and understanding their formation. The Kepler-9 system contains two Saturn-mass planets, Kepler-9b and 9c. Using evolution models of gas giants that reproduce the sizes of known transiting planets and accounting for all sources of uncertainties, we show that Kepler-9b (respectively 9c) contains M⊕ (resp. M⊕) of hydrogen and helium and M⊕ (resp. M⊕) of heavy elements. More accurate constraints are obtained when comparing planets 9b and 9c: the ratio of the total mass fractions of heavy elements are Zb/Zc = 1.02 ± 0.14, indicating that, although the masses of the planets differ, their global composition is very similar, an unexpected result for formation models. Using evolution models for super-Earths, we find that Kepler-9d must contain less than 0.1% of its mass in hydrogen and helium and predict a mostly rocky structure with a total mass between 4 and 16 M⊕.
Key words: star: individual: Kepler-9 / planetary systems / planets and satellites: physical evolution
Appendix is available in electronic form at http://www.aanda.org
© ESO, 2011
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