The Occurrence of Earth-Like Planets Around Other Stars

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The quantity η⊕, the number density of planets per star per logarithmic planetary radius per logarithmic orbital period at one Earth radius and one year period, describes the occurrence of Earth-like extrasolar planets. Here we present a measurement of η⊕ from a parameterised forward model of the (correlated) period-radius distribution and the observational selection function in the most recent (Q17) data release from the Kepler satellite. We find η⊕ = 3.9₋₁.₆⁺².²% (90% CL). We conclude that each star hosts 3.83₋₀.₆₂⁺⁰.⁷⁶ planets with P 3 yr and R 0.2 R⊕. Our empirical model for false-positive contamination is consistent with the dominant source being background eclipsing binary stars. The distribution of planets we infer is consistent with a highly-stochastic planet formation process producing many correlated, fractional changes in planet sizes and orbits.