Astronomers have discovered an exoplanet that orbits its star every 704 days, the longest known year for an exoplanet, according to Harvard-Smithsonian Center for Astrophysics.
With a star located about 1,000 light years from Earth, Kepler 421-b orbits at the "frost line" -- the crucial distance that divides rocky planets from gaseous planets.
At this distance of 110 million miles from its star, the planet is cold enough for little ice grains to form and stick together to form gaseous planets, said David Kipping, an astronomer with the center and lead author on a paper about Kepler 421-b that will be published in The Astrophysical Journal.
Within the frost line, the ice grains "boil off and you get something like Earth," Kipping told USA TODAY Network.
In our solar system, the frost line would be between Mars and Jupiter, he said.
A planet at this "special" point was expected to exist, "but we didn't really have this evidence" before Kepler 421-b's discovery, Kipping said.
Finding a planet like Kepler 421-b is rare. NASA's Kepler telescope typically spots planets that are "really, really close to their star," Kipping said. To see a planet so far away from its star requires the planet and its star to be in the telescope's field of vision, he said.
The Uranus-sized planet — about four times the size of Earth — will be one of the exoplanets astronomers will continue to study.
Although it's not a candidate for humans to live on, Kepler 421-b may have an "Earth-like" moon that is habitable, Kipping said.
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