NASA – 1,091 new transiting planet candidates have emerged from analysis of Kepler spacecraft data spanning May 2009 to September 2010, bringing the total count to 2,321 Kepler planet candidates orbiting 1,790 host stars. A clear trend toward smaller planets at longer orbital periods is evident with each new catalog release. This suggests that Earth-size planets in the habitable zone are forthcoming if, indeed, such planets are abundant.
The largest increases in planet candidates in the current release are for the smallest ones. The cumulative catalog now contains over 200 Earth-size planet candidates and more than 900 that are smaller than twice Earth-size (super-Earths), a 197% increase (compared to a 52% increase in number of candidates larger than 2 Earth radii).
There is 123% increase in planet candidates with orbital periods (time taken to orbit the star) greater than of 50-days versus 85% for candidate periods less than 50-days.
Of the 46 planet candidates found in the habitable zone (where liquid water could exist), 10 are near-Earth-size. The gains in smaller size and longer period candidates are larger than expected and indicate significant improvements the Kepler data analysis software.
The fraction of host stars with multiple candidates has grown from 17% to 20%.
The previously found dearth of short-orbital-period giant planets in multiple systems is still evident in the new planet candidate catalog. Needless to say, the unfolding story of Kepler planet candidates has major implications for theories of planetary system formation.
The data for identifying Kepler planet candidates is in the form of exquisitely precise measurement of star brightness which decreases by a minuscule amount when a planet moves in front of (transits) the star. So precise is the data that even small planets that block even less than 1/100 of 1% of the star’s brightness can be detected. In the process of identifying the new planet candidates, nearly five thousand periodic transit-like signals are vetted against known phenomena that could masquerade as transits (false positives). The most common false positives are associated with eclipsing binary stars (two stars orbiting each other and regularly blocking each others light).