Kepler-22

Kepler-22 is a Sun-like star in the northern constellation of Cygnus, the swan, that is orbited by a planet found to be unequivocally within the star's habitable zone. It is located at the celestial coordinates: Right Ascension 19^h 16^m 52.2^s, Declination +47° 53′ 3.9″.^[2] With an apparent visual magnitude of 11.7,^[3] this star is too faint to be seen with the naked eye. It can be viewed with a telescope having an aperture of at least 4 in (10 cm).^[7] The estimated distance to Kepler-22 is 644 light-years (197 parsecs).^[2]

Kepler-22

This diagram compares the Solar System to Kepler-22
Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus[1]
Right ascension	19h 16m 52.19023s[2]
Declination	+47° 53′ 03.9486″[2]
Apparent magnitude (V)	11.664[3]
Characteristics
Spectral type	G5V[4]
Astrometry
Radial velocity (Rv)	−4.50±0.51[2] km/s
Proper motion (μ)	RA: −39.589 mas/yr[2] Dec.: −66.773 mas/yr[2]
Parallax (π)	5.0627±0.0110 mas[2]
Distance	644 ± 1 ly (197.5 ± 0.4 pc)
Absolute magnitude (MV)	~5.27
Absolute bolometric magnitude (Mbol)	~4.98
Details
Mass	0.857+0.051 −0.043[5] M☉
Radius	0.869±0.011[5] R☉
Luminosity (bolometric)	0.79 ± 0.04[3] L☉
Luminosity (visual, LV)	~0.67 L☉
Temperature	5596±61[5] K
Metallicity [Fe/H]	−0.255±0.065[5] dex
Rotational velocity (v sin i)	0.6 ± 1.0[3] km/s
Age	7.0+4.0 −4.2[5] Gyr
Other designations
Gaia DR2 2127941757262806656, KOI-87, KIC 10593626, GSC 03546-02301, 2MASS J19165219+4753040[6]
Database references
SIMBAD	data
Exoplanet Archive	data
KIC	data
Extrasolar Planets Encyclopaedia	data

Stellar characteristics

Kepler-22 is slightly smaller and cooler than the Sun,^[8] with a lower abundance of elements having more mass than helium.^[3] It has a spectral type of G5V, while the luminosity class remains undetermined.^[4] This star is radiating 79%^[3] of the Sun's luminosity from its outer atmosphere at an effective temperature of 5,518 K,^[3] giving it the yellow-hued glow of a G-type star.^[9] A projected rotational velocity of 0.6 km/s^[3] suggests it has a long period of rotation. No flare activity has been detected.^[10]

Planetary system

The Kepler-22 planetary system^[5]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	<9.1 M🜨	0.812+0.011 −0.013	289.863876±0.000013	<0.72	89.764+0.025 −0.042°	2.10±0.12 R🜨

On December 5, 2011, scientists from the Kepler mission announced that an exoplanet, Kepler-22b, had been discovered orbiting in the star's habitable zone by NASA's Kepler spacecraft.^[11][12] This was significant in that it was the first relatively small exoplanet (about 2.4 R_🜨)^[12] confirmed to be orbiting within a star's habitable zone.^[13] Its size suggests that it is not likely to be a rocky planet and is more likely to be a mini-Neptune or ocean world; while its mass has not been measured, radial velocity observations have set an upper limit of 9.1 M_🜨 as of 2023^[update].^[5]