ROBERT SIEGEL, HOST:
Today NASA announced the discovery of an unprecedented number of new planets beyond our solar system. NPR's Nell Greenfieldboyce reports that scientists have confirmed the presence of more than 1,200 new worlds orbiting distant stars.
NELL GREENFIELDBOYCE, BYLINE: These alien planets were discovered with the help of NASA's Kepler space telescope. Paul Hertz is director of the Astrophysics Division at NASA Headquarters. He says when NASA launched Kepler back in 2009, no one knew if planets around other stars were common or rare.
PAUL HERTZ: We now know that exoplanets are common, that most stars in our galaxy have planetary systems and that a reasonable fraction of the stars in our galaxy has potentially habitable planets.
GREENFIELDBOYCE: Kepler was designed to search for planets by staring for years at over a hundred thousand stars. Whenever a planet passed in front of a star and blocked some of its light, Kepler would see a telltale dimming in the starlight.
Timothy Morton is a researcher at Princeton University. He says once Kepler detected a slight dimming that might mean a planet, scientists would follow up with observations using other telescopes to see if the discovery was real.
TIMOTHY MORTON: The process of verifying a candidate as a true planet has traditionally involved details, in-depth study on a case-by-case basis.
GREENFIELDBOYCE: Trouble is, that takes time and a lot of effort, so Morton developed a new, automated technique that let him quantify the probability that a Kepler signal was really a planet without having to do those cumbersome follow-up observations. Now he's announced that a slew of Kepler's observations have more than a 99 percent probability of being real planets. That means 1,284 new planets.
MORTON: So this is the most exoplanets that have ever been announced at one time.
GREENFIELDBOYCE: And it more than doubles the number of verified planets discovered by Kepler. Based on size, over 500 of the newly identified planets could be rocky planets like Earth, and nine of them orbit in their star's so-called Goldilocks zone. That's a region around a star that's not too hot or too cold for liquid water and maybe even life.
Previously, Kepler had only known of a dozen such planets. Natalie Batalha is the Kepler mission scientist at NASA's Ames Research Center. She says Kepler is giving researchers a real sense of what kind of planets are out there.
NATALIE BATALHA: We're talking about tens of billions of potentially habitable Earth-size planets out there in the galaxy.
GREENFIELDBOYCE: Next year, NASA is planning to launch another space telescope called TESS. It will be similar to Kepler but will search the entire sky to find Earthlike planets around closer, brighter stars. Astronomers should have an easier time studying those planets to learn more about what they're like and whether they might be right for life. Nell Greenfieldboyce, NPR News.
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