KOI-3158: The oldest known system of terrestrial-size planets

TL;DR

This paper reports the discovery of KOI-3158, the oldest known system of terrestrial-size planets, formed over 11 billion years ago, demonstrating that Earth-sized planets have existed throughout most of the Universe's history.

Contribution

It provides the first precise age measurement of an old, metal-poor star hosting Earth-sized planets, showing such planets formed early in the Universe.

Findings

KOI-3158 hosts five terrestrial-size planets.

The star's age is measured at approximately 11.2 billion years.

Earth-sized planets have existed for most of the Universe's history.

Abstract

The first discoveries of exoplanets around Sun-like stars have fueled efforts to find ever smaller worlds evocative of Earth and other terrestrial planets in the Solar System. While gas-giant planets appear to form preferentially around metal-rich stars, small planets (with radii less than four Earth radii) can form under a wide range of metallicities. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were far less abundant. We report Kepler spacecraft observations of KOI-3158, a metal-poor Sun-like star from the old population of the Galactic thick disk, which hosts five planets with sizes between Mercury and Venus. We used asteroseismology to directly measure a precise age of 11.2+/-1.0 Gyr for the host star, indicating that KOI-3158 formed when the Universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the Universe's 13.8-billion-year history, providing scope for the existence of ancient life in the Galaxy.