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 ^ { +0.23 } _ { -0.20 } - R _ { \oplus } planet orbits its G2 host star every 384.843 ^ { +0.007 } _ { -0.012 } days , the longest orbital period for a small ( R _ { P } < 2 R _ { \oplus } ) 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 \pm { 85 } K and a log g of 4.32 \pm { 0.09 } .
At a mean orbital separation of 1.046 ^ { +0.019 } _ { -0.015 } 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 ^ { +0.15 } _ { -0.09 } R _ { \sun } and an estimated age of \sim 6 Gyr .
Thus , Kepler-452b has likely always been in the habitable zone and should remain there for another \sim 3 Gyr .