NASA's planet-hunting Kepler space telescope may be out of commission, but the mission has yielded 715 new confirmed detections of alien worlds — thanks to a new way of looking at the probe's data.
The bonanza boosts the number of planets found beyond our solar system to nearly 1,700, said Jack Lissauer, a planetary scientist at NASA's Ames Research Center who serves as the $600 million mission's co-investigator.
"We've almost doubled just today the number of planets known to humanity," he told reporters during a teleconference Wednesday.
Kepler was launched in 2009 to detect planets among 150,000 stars in a patch of sky that straddles the constellations Lyra and Cygnus, using what's known as the transit method. That method involves looking for the faint dips in starlight that occur when a planet passes over its parent sun's disk.
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In the past, Kepler's detections have had to be verified using other methods — for example, by analyzing the gravitational effect that a planet has on the wobble of its sun. The verification was necessary because some of Kepler's detections were actually caused by one star in a multiple-star system eclipsing another.
In hundreds of cases, astronomers detected several blips in a star system — and recently, they figured out which cases couldn't possibly have been caused by eclipsing stars because such star systems would be unstable. "The fact that you can't have multiple star systems that look like planetary systems is the basis of verification by multiplicity," Lissauer explained.
That realization led to a "veritable exoplanet bonanza," he said. The 715 planets added to the list on Wednesday are distributed among 305 different star systems.
The new verification system makes it easier to confirm the existence of smaller planets, said Jason Rowe, a member of the Kepler science team who works at NASA Ames and the SETI Institute. Ninety-four percent of the newly confirmed planets are smaller than Neptune, and the number of roughly Earth-sized planets in Kepler's database rose by more than 400 percent, Rowe said.
Rowe said four of the newfound planets lie in the "habitable zone" of their star systems, where water can exist in liquid form. Those four worlds, which are all two to 2.5 times as wide as Earth, have been designated Kepler-174d, Kepler-296f, Kepler-298d and Kepler-309c, he said.
Scientific papers describing the discoveries are to be published March 10 in The Astrophysical Journal. They're already available as part of the Kepler mission's online press kit.
Kepler's planet search had to be suspended last May when the spacecraft's fine-pointing system failed, and it's not yet clear whether it can be returned to service. But MIT astronomer Sara Seager said hundreds more planets, including Earth-scale worlds, could be found in the data already collected for the mission.
"Kepler is the gift that keeps on giving," Seager said.