Planetary system
Kepler-1638 b is an exoplanet in orbit of its star, Kepler-1638, located in the constellation Cygnus. It was confirmed in 2016 as part of a study statistically validating hundreds of Kepler planets. Based on the parameters in the discovery paper, the planet is a super-Earth, with a radius of 1.87+0.33
−0.22 R🜨, and a predicted mass of 4.16 Earths. It has an orbit of 259.337±0.013 days in its system's habitable zone and orbits 0.745 AU from its star. It is the most distant known exoplanet that is considered potentially habitable.[3][14][11][12][13]
However, these parameters were estimated before the first measurement of the host star's parallax was published as part of Gaia DR2 in 2018. The Gaia parallax suggests a distance of about 1,548 parsecs (5,050 light-years),[2] much farther than the pre-Gaia estimate of about 764 parsecs (2,490 light-years).[7] This revised distance results in a significantly larger estimate of the radius of the star, and thus of the planet, with a 2018 study finding a planetary radius of 3.226+0.201
−0.315 R🜨. This would make the planet an ice giant like Neptune, and thus not potentially habitable in an Earth-like sense.[16][3]
