Kepler-421b

Kepler-421b is an exoplanet that, as of July 2014, has the longest known year of any transiting planet (704 days),[1] 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.).[2] It is the first transiting-planet found near the snow-line.

Planets with long years

Currently the known directly imaged planets are far from their star so have long years: GU-Piscium-b's year is 163,000 years long. The directly imaged planet with the shortest year is Beta-Pictoris-b with a year that takes 20 years. The transiting planets known so far are close to their stars: The transiting planet with the longest year is Kepler-421b with a year that lasts 704 days or about 2 years.[1]

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 although its mass is not known.