Terrestrial Planet Occurrence Rates for the Kepler GK Dwarf Sample

Abstract

We measure planet occurrence rates using the planet candidates discovered by the Q1-Q16 Kepler pipeline search. This study examines planet occurrence rates for the Kepler GK dwarf target sample for planet radii, 0.75 ⩽ R_p ⩽ 2.5 R⊕, and orbital periods, 50 ⩽ P_(orb) ⩽ 300 days, with an emphasis on a thorough exploration and identification of the most important sources of systematic uncertainties. Integrating over this parameter space, we measure an occurrence rate of F_0 = 0.77 planets per star, with an allowed range of 0.3 ⩽ F_0 ⩽ 1.9. The allowed range takes into account both statistical and systematic uncertainties, and values of F_0 beyond the allowed range are significantly in disagreement with our analysis. We generally find higher planet occurrence rates and a steeper increase in planet occurrence rates toward small planets than previous studies of the Kepler GK dwarf sample. Through extrapolation, we find that the one year orbital period terrestrial planet occurrence rate ζ_(1.0)= 0.1, with an allowed range of 0.01 ⩽ ζ_(1.0) ⩽ 2, where ζ_(1.0) is defined as the number of planets per star within 20% of the R_p and P_(orb) of Earth. For G dwarf hosts, the ζ_(1.0) parameter space is a subset of the larger η⊕ parameter space, thus ζ_(1.0) places a lower limit on η⊕ for G dwarf hosts. From our analysis, we identify the leading sources of systematics impacting Kepler occurrence rate determinations as reliability of the planet candidate sample, planet radii, pipeline completeness, and stellar parameters.

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