1301.0023 (Jonathan J. Swift et al.)

Characterizing the Cool KOIs IV: Kepler-32 as a prototype for the formation of compact planetary systems throughout the Galaxy    [PDF]

Jonathan J. Swift, John Asher Johnson, Timothy D. Morton, Justin R. Crepp, Benjamin T. Montet, Daniel C. Fabrycky, Philip S. Muirhead

The Kepler space telescope has opened new vistas in exoplanet discovery space by revealing populations of Earth-sized planets that provide a new context for understanding planet formation. Approximately 70% of all stars in the Galaxy belong to the diminutive M dwarf class, several thousand of which lie within Kepler's field of view, and a large number of these targets show planet transit signals. Kepler-32 is a typical star in the Kepler M dwarf sample that presents us with a rare opportunity: five planets transit this star giving us an expansive view of its architecture. All five planets of this compact system orbit their host star within a distance one third the size of Mercury's orbit with the innermost planet positioned a mere 4.3 stellar radii from the stellar photosphere. New observations limit possible false positive scenarios allowing us to validate the entire Kepler-32 system making it the richest known system of transiting planets around an M dwarf. Based on considerations of the stellar dust sublimation radius, the near period commensurability of three adjacent planets, a minimum mass protoplanetary nebula, and the volatile content inferred for the planets, we propose that the Kepler-32 planets formed at larger orbital radii and migrated inward to their present locations. The volatile content inferred for the Kepler-32 planets and order of magnitude estimates for the disk migration rates suggest these planets may have formed beyond the snow line and migrated in the presence of a gaseous disk. The Kepler-32 planets are representative of the full ensemble of planet candidates orbiting the Kepler M dwarfs for which we calculate an occurrence rate of 1.0 +/- 0.1 planet per star. The formation of the Kepler-32 planets therefore offers a plausible blueprint for the formation of one of the largest known populations of planets in our Galaxy.

View original: http://arxiv.org/abs/1301.0023