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 .
The Kepler M dwarf sample has a characteristic mass of 0.5 M _ { \odot } representing a stellar population twice as common as Sun-like stars .
Kepler-32 is a typical star in this 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 , a minimum mass protoplanetary nebula , and the near period commensurability of three adjacent 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 .
If true , this would place an upper limit on their formation time of \sim 10 Myr .
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 \pm 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 .