Kepler-421b is an exoplanet that, as of July 2014,[1] has the longest known year of any transiting planet (704 days),[2] although not as long as the planets that have been directly imaged, or many of the planets found by the radial-velocity method, or as long as some transiting planet candidates which are listed as planets in the Extrasolar Planets Encyclopaedia (KIC 5010054 b etc.).
[3] It is the first transiting-planet found near the snow-line.
Normally, at least three transits are required to confirm a planet.
Due to very high signal to noise ratio, only two transits were sufficient to validate Kepler-421b to be a real planet without additional confirmation methods.
Kepler-421b is slightly larger than Uranus, and having a mass 16.1 times[4] that of Earth, typical of an ice giant.