Kepler's First Rocky Planet: Kepler-10b

NASA's Kepler Mission uses transit photometry to determine the frequency of Earth-size planets in or near the habitable zone of Sun-like stars. The mission reached a milestone toward meeting that goal: the discovery of its first rocky planet, Kepler-10b. Two distinct sets of transit events were detected: (1) a 152 ± 4 ppm dimming lasting 1.811 ± 0.024 hr with ephemeris T [BJD] =2454964.57375^+0.00060 _-0.00082 + N*0.837495^+0.000004 _-0.000005 days and (2) a 376 ± 9 ppm dimming lasting 6.86 ± 0.07 hr with ephemeris T [BJD] =2454971.6761^+0.0020 _-0.0023 + N*45.29485^+0.00065 _-0.00076 days. Statistical tests on the photometric and pixel flux time series established the viability of the planet candidates triggering ground-based follow-up observations. Forty precision Doppler measurements were used to confirm that the short-period transit event is due to a planetary companion. The parent star is bright enough for asteroseismic analysis. Photometry was collected at 1 minute cadence for >4 months from which we detected 19 distinct pulsation frequencies. Modeling the frequencies resulted in precise knowledge of the fundamental stellar properties. Kepler-10 is a relatively old (11.9 ± 4.5 Gyr) but otherwise Sun-like main-sequence star with T _eff = 5627 ± 44 K, M _sstarf = 0.895 ± 0.060 M _sun, and R _sstarf = 1.056 ± 0.021 R _sun. Physical models simultaneously fit to the transit light curves and the precision Doppler measurements yielded tight constraints on the properties of Kepler-10b that speak to its rocky composition: M _P = 4.56^+1.17 _-1.29 M _⊕, R _P = 1.416^+0.033 _-0.036 R _⊕, and ρ_P = 8.8^+2.1 _-2.9 g cm^-3. Kepler-10b is the smallest transiting exoplanet discovered to date.

Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology.