An Earth-sized Planet in the Habitable Zone of a Cool Star

TL;DR

This paper reports the discovery of Kepler-186f, an Earth-sized planet in the habitable zone of a cool star, which could potentially support liquid water if it has an Earth-like atmosphere.

Contribution

First detection of an Earth-sized planet in the habitable zone around a cool star, expanding the known diversity of potentially habitable exoplanets.

Findings

Kepler-186f is 1.11 Earth radii.

It orbits within the star's habitable zone.

The host star is a cool, small star.

Abstract

The quest for Earth-like planets represents a major focus of current exoplanet research. While planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surface. We present the detection of Kepler-186f, a 1.11+\-0.14 Earth radius planet that is the outermost of five planets - all roughly Earth-sized - that transit a 0.47+\-0.05 Rsun star. The intensity and spectrum of the star's radiation places Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and H2O at its surface, then some of this H2O is likely to be in liquid form.