After five years of searching, researchers using data from NASA’s exoplanet-hunting Kepler spacecraft have discovered what look to be two of the most Earth-like worlds yet.

Dubbed Kepler 438 b and Kepler 442 b, both planets appear to be rocky and orbit in the not-too-hot, not-too-cold habitable zones of their stars where liquid water can exist in abundance. Astronomers announced the planets along with six other newfound small, temperate worlds today at a meeting of the American Astronomical Society in Seattle. Their findings will be published in The Astrophysical Journal. The discoveries double the number of known potentially habitable exoplanets. They also push Kepler’s tally of vetted, confirmed worlds to just over 1,000, marking a milestone in the mission’s epochal search for alien Earths.

Both planets are many hundreds of light-years away and orbit stars smaller and dimmer than our sun. Like most of Kepler’s finds, they were discovered via transits—the shadows they cast toward our solar system as they cross the blazing faces of their stars. Transits allow astronomers to measure a planet’s size, orbit and exposure to starlight. Kepler 438 b is only about 12 percent larger than Earth, and basks in 40 percent more starlight; Kepler 442 b is 30 percent larger and receives about 30 percent less light. Both spheres may be somewhat warmer than Kepler’s two previous premier rocky worlds, Kepler 186 f and Kepler 62 f, each of which gets significantly less starlight—similar to that received by Mars. “We can’t say for sure whether these planets are truly habitable—only that they are promising candidates for habitability,” says study co-author David Kipping, an astronomer at the Harvard–Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass.

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