KEPLER'S FIRST ROCKY PLANET: KEPLER-10b

Abstract

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 = 0.895 ± 0.060 M _☉, and R = 1.056 ± 0.021 R _☉. 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.