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American Astronomical Society, Astrophysical Journal, 2(745), p. 120, 2012

DOI: 10.1088/0004-637x/745/2/120

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Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star

Journal article published in 2012 by David G. Koch, Thomas N. Gautier Iii, William J. Borucki, Natalie Batalha, Stephen T. Bryson, Jason Rowe, Francois Fressin, Guillermo Torres, Douglas A. Caldwell, Jørgen Christensen-Dalsgaard, William D. Cochran, Edna DeVore, Thomas N. Gautier, John C. Geary, Ronald Gilliland and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an asteroseismic analysis of the Kepler photometry, leading to an estimated mass and radius of 0.970 ± 0.060 M_☉ and 0.979 ± 0.020 R_☉. The depth of 492 ± 10 ppm for the three observed transits yields a radius of 2.38 ± 0.13 Re for the planet. The system passes a battery of tests for false positives, including reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A full BLENDER analysis provides further validation of the planet interpretation by showing that contamination of the target by an eclipsing system would rarely mimic the observed shape of the transits. The final validation of the planet is provided by 16 radial velocities (RVs) obtained with the High Resolution Echelle Spectrometer on Keck I over a one-year span. Although the velocities do not lead to a reliable orbit and mass determination, they are able to constrain the mass to a 3σ upper limit of 124 M_⊕, safely in the regime of planetary masses, thus earning the designation Kepler-22b. The radiative equilibrium temperature is 262 K for a planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is a rocky planet, it is the first confirmed planet with a measured radius to orbit in the habitable zone of any star other than the Sun.