Vol. 531In section 10. Planets and planetary systems

The multiple planets transiting Kepler-9. I. Inferring stellar properties and planetary compositions

The discovery of multiple transiting planetary systems offers new possibilities for characterizing exoplanets. 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, the authors derive the hydrogen, helium, and heavy element contents of the two planets and find that, although the masses of the planets differ, their global composition is very similar, and is an unexpected result for formation models. Using evolution models for super-Earths, they predict that Kepler-9d has a mostly rocky structure with a total mass between 4 and 16 Earth masses.