Terrestrial, Habitablezone Exoplanet Frequency from Kepler
Abstract
Data from Kepler's first 136 days of operation are analyzed to determine the distribution of exoplanets with respect to radius, period, and hoststar spectral type. The analysis is extrapolated to estimate the percentage of terrestrial, habitablezone (HZ) exoplanets. The Kepler census is assumed to be complete for bright stars (magnitude <14.0) having transiting planets >0.5 Earth radius and periods <42 days. It is also assumed that the size distribution of planets is independent of orbital period and that there are no hidden biases in the data. Six significant statistical results are found: there is a paucity of small planet detections around faint target stars, probably an instrumental effect; the frequency of midsize planet detections is independent of whether the host star is bright or faint; there are significantly fewer planets detected with periods <3 days, compared to longer periods, almost certainly an astrophysical effect; the frequency of all planets in the population with periods <42 days is 29%, broken down as terrestrials 9%, ice giants 18%, and gas giants 3%; the population has a planet frequency with respect to period which follows a powerlaw relation dN/dP ~ P ^{β  1}, with β ~= 0.71 ± 0.08; and an extrapolation to longer periods gives the frequency of terrestrial planets in the HZs of FGK stars as η_{⊕} ~= (34 ± 14)%. Thus about onethird of FGK stars are predicted to have at least one terrestrial, HZ planet.
 Publication:

The Astrophysical Journal
 Pub Date:
 January 2012
 DOI:
 10.1088/0004637X/745/1/20
 arXiv:
 arXiv:1109.4682
 Bibcode:
 2012ApJ...745...20T
 Keywords:

 astronomical databases: miscellaneous;
 planets and satellites: detection;
 stars: statistics;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 27 pages, 5 figures