'Kepler-186f,' New Earth-Like Planet: Rocky Planet, Discovered In ‘Habitable Zone’ Where High Noon Is Like Our Sunset
It took NASA's Kepler Space Telescope measuring the brightness of more than 150,000 stars, but there it is: astronomers have discovered the first Earth-size planet orbiting a star in a "habitable zone" -- the proper distance an orbiting planet has to be from its sun in order to allow liquid to pool on the planet's surface. Kepler-186f is such a planet, and the fact that it's 500 light years away has not dampened the enthusiasm of NASA, whose Astrophysics Division director Paul Hertz, hails the discovery, described in Friday's issue of Science, as "a significant step toward finding worlds like our planet Earth." While Kepler-186f is not the first planet to be found in a habitable zone, it is the first one about Earth's size: The other planets are all at least 40 percent larger than our own.
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It may have less inviting terrain and weather, though. A planet Kepler-186f's size is likely to be rocky, previous research suggests. Kepler-186f orbits a star half the size and mass of our sun once every 130 days and receives one-third the energy from its star that Earth gets from the sun, placing it nearer the outer edge of the habitable zone: On the surface of Kepler-186f, the brightness of its star at high noon is only as bright as our sun appears to us about an hour before sunset.
Kepler-186f's sun is a red dwarf, like 70 percent of the stars in the Milky Way. Because red dwarfs are so commonplace in the universe, "the finding could open a wide new hunting ground for extraterrestrial life," a Science editorial accompanying the article says. Kepler-186f is not alone in its so-called Kepler-186 solar system: Four other planets about 1 1/2 times the size of the earth, whip around their sun every four, seven, 13, and 22 days. Their proximity to the sun makes them too hot for life, though.
"Finding a habitable zone planet comparable to Earth in size is a major step forward," said Elisa Quintana, research scientist at the SETI Institute at NASA's Ames Research Center in Moffett Field, Calif., and lead author of the paper. Astronomers are already planning looking for planets even closer to our size orbiting even more decidedly inside a habitable zone.
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