Hot Big Planets Kepler Survey: Measuring the Repopulation Rate of the Shortest-Period Planets

Abstract

By surveying new fields for the shortest-period "big" planets, the Kepler spacecraft could provide the statistics to more clearly measure the occurrence distributions of giant and medium planets. This would allow separate determinations for giant and medium planets of the relationship between the inward rate of tidal migration of planets and the strength of the stellar tidal dissipation (as expressed by the tidal quality factor Q). We propose a "Hot Big Planets Survey" to find new big planets to better determine the planet occurrence distribution at the shortest period. We call planets that Kepler will be able to find as "big", for the purpose of comparing the distribution of giant and medium planets (above and below 8 earth radii). The distribution of planets from one field has been interpreted to show that the shortest period giant planets are at the end of an ongoing flow of high eccentricity migration, likely from scattering from further out. The numbers of planets at these short periods is still small, leaving uncertainty over the result that the distribution shows the expected power index for inward tidal migration. The current statistics make it hard to say whether the presence of more giant planets at the shortest periods despite there being more medium planets at most periods indicates a greater migration of giant than medium planets. We propose a repurposed Kepler mission to make enough 45-day observations to survey 10 times as many stars as in the survey of the original field, to survey for planets with periods of up to fifteen days with at least three transits. The current statistics make it hard to say whether the presence of more giant planets at the shortest periods despite there being more medium planets at most periods indicates a greater migration of giant than medium planets.