Alien worlds, just like home
Harvard astronomers, working as part of NASA’s Kepler mission, have detected the first Earth-sized planets orbiting a distant star, a milestone in the hunt for alien worlds that brings scientists a step closer to their ultimate goal of finding a twin to Earth. Described in the Dec. 20 issue of the journal Nature, the two planets, dubbed Kepler-20e and Kepler-20f, are the smallest planets found by the Kepler mission to date. They have diameters of 6,900 miles and 8,200 miles — equivalent to 0.87 times Earth (slightly smaller than Venus) and 1.03 times Earth. These worlds are expected to have rocky compositions, so their masses should be, respectively, approximately 1.7 and 3 times Earth’s. “The goal of Kepler is to find Earth-sized planets in the habitable zone. Proving the existence of Earth-sized exoplanets is a major step toward achieving that goal,” said Francois Fressin, a research associate at the Harvard-Smithsonian Center for...