Kepler-22b: A 2.4 EARTH-RADIUS PLANET IN THE HABITABLE ZONE OF A SUN-LIKE STAR

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 ± 10ppm 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 obtained with HIRES on Keck 1 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 262K 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.

Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin

“…The radii of known transiting planets with masses close to 0.1 M Jup range from 0.21 R Jup (Kepler-22 b, Borucki et al 2012) to 0.73 R Jup (Kepler-35(AB) b, Welsh et al 2012). If the postulated planet transits the host star, the corresponding flux drop is between 0.02% and 0.2%.…”

Spectroscopy of planetary atmospheres in our Galaxy

“…close to temperate. Kepler-22b, a transiting object with a 2.4 Earth radii, has been discovered around a solar-type star with magnitude V = 12, at 0.85 AU (Borucki et al 2012). Only upper limits of its mass have been derived but the size suggests a small Neptune.…”

Constraints on the Habitability of Extrasolar Moons

“…Extrasolar habitable moons could be much more numerous than planets. In her IAU talk on Aug. 28, Natalie Batalha has shown the "Periodic (Borucki et al 2012) and the detection of Kepler-47 c in the IHZ of a stellar binary system (Orosz et al 2012) have shown that, firstly, adequate host planets exist and, secondly, their characterization is possible. Figure 1 displays a hypothetical, inhabited Earth-sized moon about Kepler-22 b in an orbit as wide as Europa's semi-major axis about Jupiter.…”

“…For reference, the Earth's outward heat flow is 0.065 W/m 2 through the continents and 0.1 W/m 2 through the ocean crust (Zahnle et al 2007). Parametrization of the star-planet system follows Borucki et al (2012). In the left panel, the moon's orbit about the planet is assumed to be coplanar with the circumstellar orbit, i.e.…”