Small planets are common: evidence from the Eta-Earth Survey and the Kepler mission

Andrew Howard
UC Berkeley


The architectures of extrasolar planetary systems provide key properties that trace the processes of planet formation and evolution. Until recently, Jovian-size planets provided nearly all of the observational constraints. I will describe two new probes of the properties of small (sub-Jovian) planets. First, using Doppler measurements from NASA-UC Eta-Earth Survey at Keck, our group measured the mass function of planets from Jupiter-mass down through super-Earths. This mass function rises steeply toward lower mass and, extrapolating down to one Earth mass, we predict that one in four Sun-like stars have a close-in planet of approximately Earth mass. Second, the distribution of close-in transiting planets detected by the Kepler space telescope paints a similar picture of rising numbers of small planets. The Kepler discoveries also demonstrate that small planets are more common around low-mass stars and at greater orbital distances. My talk will describe how these patterns of planet occurrence, including the notable absence of the predicted desert of close-in low-mass planets, offer key constraints on theories of planet formation and migration.