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arXiv · 1301.0023

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

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

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.

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Jonathan J. Swift, John Asher Johnson, Timothy D. Morton, Justin R. Crepp, Benjamin T. Montet, Daniel C. Fabrycky, Philip S. Muirhead. 2012-12-31. Characterizing the Cool KOIs IV: Kepler-32 as a prototype for the formation of compact planetary systems throughout the Galaxy. https://doi.org/10.1088/0004-637x%2F764%2F1%2F105

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