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NASA's Kepler mission uncovers 461 more potential planets to check out

An artist's illustration represents the variety of planets being detected by NASA's Kepler spacecraft, from worlds smaller than Earth up to Jupiter-type gas giants.
An artist's illustration represents the variety of planets being detected by NASA's Kepler spacecraft, from worlds smaller than Earth up to Jupiter-type gas giants.C. Pulliam and D. Aguilar / CfA

NASA's Kepler space telescope has uncovered another 461 potential new planets, most of which are the size of Earth or a few times larger, scientists said Monday.

The announcement brings Kepler's head count to 2,740 candidate new worlds, 105 of which have been confirmed.

"Two years ago we had around 1,200 candidate planet objects. A year later, we added a significant number of new objects and saw the trend of huge numbers of very small planets ... twice the size of Earth and smaller," Kepler astronomer Christopher Burke told a news conference webcast from the American Astronomical Society conference in Long Beach, Calif.

With the addition of 461 new candidate planets, collected over 22 months of Kepler telescope observations, the proliferation of smaller planets continues.

The new targets include KOI-172.02, a planet candidate that's about 1.5 times bigger than Earth and circles its sunlike parent star in a 242-day orbit. At that distance, liquid water, believed to be necessary for life, could exist on the potential planet's surface.

A Jupiter-sized planet known as PH2 b, discovered by citizen scientists participating in the Planet Hunters project, lies within its parent star's habitable zone.

"This is just a first step toward finding a habitable world elsewhere," Ji Wang, a postdoctoral researcher at Yale University and the lead author of a paper about PH2 b, said in a news release. "Any moon around this newly discovered, Jupiter-sized planet might be habitable. It’s very similar to what was depicted in the movie ‘Avatar’ — the habitable moon Pandora around a giant planet, Polyphemus.”

The Planet Hunters group also reported finding 42 candidate planets, including 15 that lie within habitable zones.

The goal of the Kepler mission, which began in 2009, is to determine how many stars in the Milky Way galaxy have an Earth-sized planet orbiting in so-called habitable zones, where water can exist on its surface.

"You need very specific conditions to have liquid water. You can't have your planet too close to your star where it's too hot. You can't have it too far away for the planet conditions to be too cold. We're trying to find these planets in this very specific habitable zone," said Burke, who is with the SETI Institute in Mountain View, Calif.

The Kepler telescope works by tracking slight decreases in the amount of light coming from 160,000 target stars caused by a planet or planets passing by, or transiting, relative to the telescope's point of view.

Earth-sized planets located about where Earth orbits the sun would take 365 days to circle their parent star. Those located closer, in Mercury-type 88-day orbits, transit more frequently. Scientists need at least two and preferably three or more cycles to determine whether an apparent transit is real or some other phenomena.

The Kepler roster also boosts the number of multiplanet systems. Of the 2,740 objects, 299 are in dual-planet systems, 112 are in triplets, 44 are part of four-planet systems, 11 systems have five planets and one system has six planets.

More about the planet quest:

This report includes information from NBC News. Reuters content: Copyright Thomson Reuters 2012. Check for restrictions at