Nearly 95 percent of these planets are smaller than Neptune, which is almost four times the size of Earth. This discovery marks a significant increase in the number of known small-sized planets more akin to Earth than previously identified exoplanets, which are planets outside our solar system.
"The Kepler team continues to amaze and excite us with their planet hunting results," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate in Washington. "That these new planets and solar systems look somewhat like our own, portends a great future when we have the James Webb Space Telescope in space to characterize the new worlds.”
Since the discovery of the first planets outside our solar system roughly two decades ago, verification has been a laborious planet-by-planet process. Now, scientists have a statistical technique that can be applied to many planets at once when they are found in systems that harbor more than one planet around the same star.
To verify this bounty of planets, a research team co-led by Jack Lissauer, planetary scientist at NASA's Ames Research Center in Moffett Field, Calif., analyzed stars with more than one potential planet, all of which were detected in the first two years of Kepler's observations -- May 2009 to March 2011.
The research team used a technique called verification by multiplicity, which relies in part on the logic of probability. Kepler observes 150,000 stars, and has found a few thousand of those to have planet candidates. If the candidates were randomly distributed among Kepler's stars, only a handful would have more than one planet candidate. However, Kepler observed hundreds of stars that have multiple planet candidates. Through a careful study of this sample, these 715 new planets were verified.
These multiple-planet systems are fertile grounds for studying individual planets and the configuration of planetary neighborhoods. This provides clues to planet formation.
"From this study we learn planets in these multi-systems are small and their orbits are flat and circular -- resembling pancakes -- not your classical view of an atom," said Jason Rowe, research scientist at the SETI Institute in Mountain View, Calif., and co-leader of the research. "The more we explore the more we find familiar traces of ourselves amongst the stars that remind us of home."
This latest discovery brings the confirmed count of planets outside our solar system to nearly 1,700. As we continue to reach toward the stars, each discovery brings us one step closer to a more accurate understanding of our place in the galaxy.
Launched in March 2009, Kepler is the first NASA mission to find potentially habitable Earth-size planets. Discoveries include more than 3,600 planet candidates, of which 961 have been verified as bona-fide worlds.
The findings papers will be published March 10 in The Astrophysical Journal and are available for download at: