Kepler-421b

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.

Kepler-421b

Discovery
Discovery site	Kepler telescope
Discovery date	2014
Detection method	Transit
Orbital characteristics
Semi-major axis	1.219 AU (182,400,000 km)
Orbital period (sidereal)	704.1984 d
Inclination	89.965
Star	Kepler-421
Physical characteristics
Mean radius	4.16 R🜨
Mass	16.1 M🜨

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.