The first Earth-sized Rocky Planet

Astronomers have discovered Kepler-78b, the first Earth-sized planet outside the solar system that has a rocky composition like that of Earth. The exoplanet whizzes around its host star every 8.5 hours, making it a blazing inferno and not suitable for life as we know it. David A. Aguilar (CfA)

Kepler-78b is about 20 percent larger than Earth and is 70% more massive.

“The news arrived in grand style with the message: ‘Kepler-10b has a baby brother,'” said Natalie Batalha, Kepler mission scientist at NASA’s Ames Research Center in Moffett Field, Calif. Batalha led the team that discovered Kepler-10b, a larger but also rocky planet identified by the Kepler spacecraft.

“The message expresses the joy of knowing that Kepler’s family of exoplanets is growing,” Batalha reflects. “It also speaks of progress. The Doppler teams are attaining higher precision, measuring masses of smaller planets at each turn. This bodes well for the broader goal of one day finding evidence of life beyond Earth.”

Kepler-78b was discovered using data from NASA’s Kepler space telescope, which for four years simultaneously and continuously monitored more than 150,000 stars looking for telltale dips in their brightness caused by crossing, or transiting, planets.

Two independent research teams then used ground-based telescopes to confirm and characterize Kepler-78b. To determine the planet’s mass, the teams employed the radial velocity method to measure how much the gravitation tug of an orbiting planet causes its star to wobble. Kepler, on the other hand, determines the size or radius of a planet by the amount of starlight blocked when it passes in front of its host star.