Astronomers using NASA’s Kepler mission have detected two Earth-sized planets orbiting a distant star. This discovery marks a milestone in the hunt for alien worlds, since it brings scientists one step closer to their ultimate goal of finding a twin Earth.
“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 of the Harvard-Smithsonian Center for Astrophysics (CfA).
The paper describing the finding will be published in the journal Nature.
The two planets, dubbed Kepler-20e and 20f, are the smallest planets found 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 less than 1.7 and 3 times Earth’s.