Kepler-78 and the Ultra-Short-Period Planets

Understand

Compared to the Earth, the exoplanet Kepler-78b has a similar size (1.2 $R_\oplus$) and an orbital period a thousand times shorter (8.5 hours).

• It is currently the smallest planet for which the mass, radius, and dayside brightness have all been measured.
• Kepler-78b is an exemplar of the ultra-short-period (USP) planets, a category defined by the simple criterion $P_{\rm orb} < 1$ day.
• We describe our Fourier-based search of the Kepler data that led to the discovery of Kepler-78b, and review what has since been learned about the population of USP planets.