PROBABLE SPIN-ORBIT ALIGNED SUPER-EARTH PLANET CANDIDATE KOI2138

Abstract

We use rotational gravity darkening in the disk of Kepler star KOI-2138 to show that the orbit of transiting planet candidate KOI-2138.01 has a low projected spin-orbit alignment of . KOI-2138.01 is just the second super-Earth with a measured spin-orbit alignment after 55 Cancri e, and the first to be aligned. With a 23.55 days orbital period, KOI-2138.01 may represent the tip of a future iceberg of solar-system-like terrestrial planets having intermediate periods and low-inclination circular orbits.