A hot Mars-sized exoplanet transiting an M dwarf

Abstract

We validate the planetary nature of an ultra-short period planet orbiting the M dwarf KOI-4777. We use a combination of space-based photometry from Kepler, high-precision, near-infrared Doppler spectroscopy from the Habitable-zone Planet Finder, and adaptive optics imaging to characterize this system. KOI-4777.01 is a Mars-sized exoplanet (${\mathrm{R}}_p=0.51\pm 0.03R_{\oplus }$) orbiting the host star every 0.412-days ($\sim 9.9$-hours). This is the smallest validated ultra-short period planet known and we see no evidence for additional massive companions using our HPF RVs. We constrain the upper $3\ddot{I}ƒ$ mass to $M_p<0.34{\mathrm{M}}_{\oplus }$ by assuming the planet is less dense than iron. Obtaining a mass measurement for KOI-4777.01 is beyond current instrumental capabilities.

25 pages, 8 figures, accepted for publication in AJ