Institute of Astronomy

Earth-sized Exoplanets

SpeakerTalk DateTalk Series
Andrew Howard29 July 2014Across HR 2014 Talks


The Kepler Mission has taught us that Earth-sized planets in the Habitable Zones of Sun-like stars are common and that most Earth-sized planets have rocky compositions. Three recent results highlight these remarkable properties of Earth-size planets. First, our team measured the mass of the planet Kepler-78b, the only Earth-sized planet with a measured mass and radius outside of the Solar System. The bulk density of 5 grams per cubic centimeter suggests a rocky composition with an insubstantial atmosphere, similar to Earth. In a separate project, we showed that high densities are common for small exoplanets. Based on three years of Doppler measurements of the masses of dozens of Kepler planets, we showed that planets smaller than about 1.5 times Earth size are mostly rocky, while thick gas atmospheres envelop larger planets. Finally, we re-analyzed the Kepler photometry to determine an independent, calibrated catalog of planets, including Earth-sized planets in the Habitable Zones of Sun-like stars (GK dwarfs). We calibrated the survey completeness using injection-and-recovery tests of transit signals into Kepler photometry using our custom-built TERRA pipeline. Combining our planet catalog and completeness estimate we find that 22 percent of Sun-like stars have a planet that is 1-2 times the size of Earth orbiting in the Habitable Zone. Warm, Earth-sized planets appear to be common.