Courtesy NASA/JPL-Caltech/T. PyleNASA announced this week the discovery of two Earth-sized planets orbiting a star 1000 light-years away in the constellation Lyra. The star system, called Kepler 20, is orbited by five planets. The two planets of interest, named Kepler-20e and Kepler-20f, are the first exoplanets their size to be discovered around another star resembling our own.
Francois Fressin, the lead author of the study which appears in the journal Nature, said the Kepler mission's main goal is to discover Earth-sized planets located in the habitable zone of other star systems. "This discovery demonstrates for the first time that Earth-size planets exist around other stars, and that we are able to detect them,” Fressin said.
Kepler 20e is slightly smaller than Venus, while Kepler-20f is slightly larger than Earth. The exoplanets' host star is smaller than the Sun and a bit cooler in temperature, however, the orbits of Kepler-20e and 20f are closer to their star than Mercury is to our sun, which makes them far too hot to support liquid water and too inhospitable to support life.
But the discovery is a big step in the three-and-a-half year Kepler mission, which uses ground-based telescopes and space telescopes to search out possible planet candidates.