Characteristics of Planetary Candidates Observed by Kepler . Ii. Analysis of the First Four Months of Data

Abstract

On 2011 February 1 the Kepler mission released data for 156,453 stars observed from the beginning of the science observations on 2009 May 2 through September 16. There are 1235 planetary candidates with transit-like signatures detected in this period. These are associated with 997 host stars. Distributions of the characteristics of the planetary candidates are separated into five class sizes: 68 candidates of approximately Earth-size (R-p < 1.25 R-circle plus), 288 super-Earth-size (1.25 R-circle plus <= R-p < 2 R-circle plus), 662 Neptune-size (2 R-circle plus <= R-p < 6 R-circle plus), 165 Jupiter-size (6 R-circle plus <= R-p < 15 R-circle plus), and 19 up to twice the size of Jupiter (15 R-circle plus <= R-p < 22 R-circle plus). In the temperature range appropriate for the habitable zone, 54 candidates are found with sizes ranging from Earth-size to larger than that of Jupiter. Six are less than twice the size of the Earth. Over 74% of the planetary candidates are smaller than Neptune. The observed number versus size distribution of planetary candidates increases to a peak at two to three times the Earth-size and then declines inversely proportional to the area of the candidate. Our current best estimates of the intrinsic frequencies of planetary candidates, after correcting for geometric and sensitivity biases, are 5% for Earth-size candidates, 8% for super-Earth-size candidates, 18% for Neptune-size candidates, 2% for Jupiter-size candidates, and 0.1% for very large candidates; a total of 0.34 candidates per star. Multi-candidate, transiting systems are frequent; 17% of the host stars have multi-candidate systems, and 34% of all the candidates are part of multi-candidate systems.