2015AJ....150...56J

We report on the discovery and validation of Kepler-452b, a transiting planet identified by a search through the 4 years of data collected by NASA's Kepler Mission. This possibly rocky 1.63_–0.20^+0.23 planet orbits its G2 host star every 384.843_–0.012^+0.007 days, the longest orbital period for a small (R_p < 2 R_⊕) transiting exoplanet to date. The likelihood that this planet has a rocky composition lies between 49% and 62%. The star has an effective temperature of 5757±85 K and a log g of 4.32±0.09. At a mean orbital separation of 1.046_–0.015^+0.019 AU, this small planet is well within the optimistic habitable zone of its star (recent Venus/early Mars), experiencing only 10% more flux than Earth receives from the Sun today, and slightly outside the conservative habitable zone (runaway greenhouse/maximum greenhouse). The star is slightly larger and older than the Sun, with a present radius of 1.11_–0.099^+0.15 R_☉ and an estimated age of ∼6 Gyr. Thus, Kepler-452b has likely always been in the habitable zone and should remain there for another ∼3 Gyr.