Kepler-10b

Kepler-10b was the first rocky planet confirmed beyond the Solar System by the Kepler Space Telescope. Its discovery, announced on January 10, 2011, came after months of data gathered as part of the NASA-led Kepler Mission, which searches for Earth-like planets that cross in front of their stars.

The planet orbits the star Kepler-10, located 560 light-years away in the constellation Draco. Kepler-10 is roughly the same size as the Sun and about 12 billion years old. Kepler-10b was the first planet found in this star’s orbit, earning the designation “b.” The star itself was named after the Kepler Mission.

The planet was detected using the transit method, which monitors a star’s brightness for regular dips caused by a planet passing in front of it. Kepler-10 dimmed by one part in ten thousand every 0.83 days. The first transits were observed in July 2009, based on data collected from May 2009 to January 2010. Kepler-10 was the first star in the telescope’s field identified as likely to host a small transiting planet, making it a priority for ground-based follow-up. Radial velocity measurements from the Keck I telescope, taken between August 2009 and August 2010, confirmed the planet’s existence and allowed its mass to be determined. The discovery was announced on January 10, 2011.

In September 2011, the detection of a secondary transit and phases was announced, allowing scientists to determine the planet’s temperature and albedo. This was the first terrestrial exoplanet with observed phases, made possible by extreme temperature differences between its day and night sides and the intense starlight it receives.

The discovery excited astronomers, who hoped to learn about the formation and structure of Earth-sized rocky planets. Geoff Marcy of the University of California at Berkeley called it “among the most profound scientific discoveries in human history” and said it “will go into every textbook worldwide,” describing Kepler-10b as “a bridge between the gas giant planets we’ve been finding and the Earth itself.” Diana Valencia at the University of Côte d’Azur considered it more of a “super-Mercury” than a super-Earth, given its physical traits.

Kepler-10b has a mass of 3.72 ± 0.42 Earth masses and a radius of 1.47 Earth radii. Its density is high, and it orbits its star in less than a day, at less than one-twentieth the distance from Mercury to the Sun.