Kepler-1638
G-type star in the constellation Cygnus
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Kepler-1638 is a G-type subgiant star located about 5,000 light years away in the constellation of Cygnus.[1] One known exoplanet has been found orbiting the star: Kepler-1638b.[11][12][13][14]As of January 2021, Kepler-1638 is the farthest star with a known exoplanet orbiting in the habitable zone.[15]
Constellation where Kepler-1638 is located | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cygnus[1] |
| Right ascension | 19h 41m 55.76712s[2] |
| Declination | +48° 31′ 27.9998″[2] |
| Apparent magnitude (V) | 14.769±0.206[3] |
| Characteristics | |
| Evolutionary stage | subgiant[2] |
| Spectral type | G[4] |
| Apparent magnitude (J) | 13.550±0.023[5] |
| Apparent magnitude (H) | 13.204±0.024[5] |
| Apparent magnitude (K) | 13.138±0.035[5] |
| Variable type | Planetary transit[3] |
| Astrometry | |
| Proper motion (μ) | RA: −5.092 mas/yr[2] Dec.: +5.839 mas/yr[2] |
| Parallax (π) | 0.6462±0.0165 mas[2] |
| Distance | 5,000 ± 100 ly (1,550 ± 40 pc) |
| Details | |
| Mass | 1.03[6] M☉ |
| Radius | 1.62[6] R☉ |
| Luminosity | 2.59[6] L☉ |
| Surface gravity (log g) | 4.03[6] cgs |
| Temperature | 5,745[6] K |
| Metallicity [Fe/H] | −0.76+0.32 −0.26[7] dex |
| Rotation | 27.7 days[8] |
| Rotational velocity (v sin i) | 2.25[9] km/s |
| Age | 5.7+5.1 −2.6[7] Gyr |
| Other designations | |
| KOI-5856, KIC 11037818, 2MASS J19415577+4831280[10] | |
| Database references | |
| SIMBAD | data |
Planetary system
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ~4.16 M🜨 | 0.745+0.021 −0.020 |
259.33683±0.01303 | — | 89.9954+0.0021 −0.0844° |
1.87+0.33 −0.22 R🜨 |
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]
