Transits and Occultations of an Earth-Sized Planet in an 8.5-Hour Orbit

TL;DR

This paper reports the discovery of an Earth-sized planet with an extremely short 8.5-hour orbit around a G-type star, enabling detailed study of its reflected light and thermal emission.

Contribution

It presents the detection and confirmation of a very short-period Earth-sized exoplanet using Kepler data, highlighting its unique observational opportunities.

Findings

Detected an Earth-sized planet in an 8.5-hour orbit.

Observed reflected and reprocessed light from the planet.

Estimated the planet's dayside temperature between 2300 K and 3100 K.

Abstract

We report the discovery of an Earth-sized planet ($1.16\pm 0.19 R_\oplus$) in an 8.5-hour orbit around a late G-type star (KIC 8435766, Kepler-78). The object was identified in a search for short-period planets in the {\it Kepler} database and confirmed to be a transiting planet (as opposed to an eclipsing stellar system) through the absence of ellipsoidal light variations or substantial radial-velocity variations. The unusually short orbital period and the relative brightness of the host star ($m_{\rm Kep}$ = 11.5) enable robust detections of the changing illumination of the visible hemisphere of the planet, as well as the occultations of the planet by the star. We interpret these signals as representing a combination of reflected and reprocessed light, with the highest planet dayside temperature in the range of 2300 K to 3100 K. Follow-up spectroscopy combined with finer sampling photometric observations will further pin down the system parameters and may even yield the mass of the planet.