Article · Wikipedia archive · Last revised Jun 30, 2026

Kepler-18

Kepler-18 is a star with a system of three exoplanets, positioned in the northern Constellation of Cygnus. It has an apparent visual magnitude of 14.0, requiring a telescope to view. Based on parallax measurements, it is located at a distance of approximately 1,430 light-years (440 pc). It is drifting closer with a line of sight velocity component of −18.4 km/s.

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Kepler-18
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus1
Right ascension 19h 52m 19.0688s2
Declination +44° 44′ 46.808″2
Apparent magnitude (V) 14.03
Characteristics
Evolutionary stage main sequence2
Spectral type G7
Astrometry
Radial velocity (Rv)−18.40±0.024 km/s
Proper motion (μ) RA: −1.436(14) mas/yr2
Dec.: −20.341(14) mas/yr2
Parallax (π)2.2804±0.0168 mas2
Distance1,430 ± 10 ly
(439 ± 3 pc)
Details5
Mass0.972 ± 0.042 M☉
Radius1.108 ± 0.051 R☉
Luminosity0.93 L☉
Surface gravity (log g)4.32 ± 0.12 cgs
Temperature5,383 ± 44 K
Metallicity [Fe/H]0.19 ± 0.06 dex
Rotational velocity (v sin i)<4 km/s
Age10.0 ± 2.3 Gyr
Other designations
KOI-137, KIC 8644288, 2MASS J19521906+4444467, Gaia DR2 20792955832821649926
Database references
SIMBADdata
Exoplanet Archivedata
Comparative sizes of Earth, Kepler-18 b and Jupiter source ↗

Kepler-18 is a star with a system of three exoplanets, positioned in the northern Constellation of Cygnus. It has an apparent visual magnitude of 14.0,3 requiring a telescope to view. Based on parallax measurements, it is located at a distance of approximately 1,430 light-years (440 pc). It is drifting closer with a line of sight velocity component of −18.4 km/s.4

This is an older star with an estimated age of around ten billion years. It has similar properties to the Sun with almost the same mass and a 10% larger radius. The star is radiating 93% of the Sun's luminosity from its photosphere at an effective temperature of 5,383 K.5

Planetary system

The star is orbited by 3 confirmed transiting planets, announced in 2011.5 In 2021, it was found the orbital plane of Kepler-18d is slowly changing, likely under the gravitational influence of the additional giant planet.7

The Kepler-18 planetary system58
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination
(°) 		Radius
b 6.9 ± 3.4 M🜨 0.0447 ± 0.0006 3.504725 ± 0.000028 — 84.92 ± 0.26 2.00 ± 0.10 R🜨
c 17.3 ± 1.9 M🜨 0.0752 ± 0.0011 7.6415716 — 87.68 ± 0.22 5.49 ± 0.26 R🜨
d 16.4 ± 1.4 M🜨 0.1172 ± 0.0017 14.858941 — 88.07 ± 0.1 6.98 ± 0.33 R🜨
References

References

  1. Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
  2. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. Zacharias, N. (2012). The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4). VizieR On-line Data Catalog. Vol. 1322. Bibcode:2012yCat.1322....0Z.
  4. Jönsson, Henrik; et al. (August 17, 2020). "APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South". The Astronomical Journal. 160 (3). American Astronomical Society: 120. arXiv:2007.05537. Bibcode:2020AJ....160..120J. doi:10.3847/1538-3881/aba592. ISSN 0004-6256.
  5. Cochran, William D.; et al. (2011). "Kepler 18-b, c, and d: A System Of Three Planets Confirmed by Transit Timing Variations, Lightcurve Validation, Spitzer Photometry and Radial Velocity Measurements". The Astrophysical Journal Supplement Series. 197 (1): 7. arXiv:1110.0820. Bibcode:2011ApJS..197....7C. doi:10.1088/0067-0049/197/1/7. S2CID 16505452.
  6. "Kepler-18". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 25 January 2018.
  7. Shahaf, Sahar; Mazeh, Tsevi; Zucker, Shay; Fabrycky, Daniel (2021), "Systematic search for long-term transit duration changes in Kepler transiting planets", Monthly Notices of the Royal Astronomical Society, 505 (1): 1293–1310, arXiv:2105.04318, Bibcode:2021MNRAS.505.1293S, doi:10.1093/mnras/stab1359
  8. Montet, Benjamin T.; Johnson, John Asher (2013), "Model-Independent Stellar and Planetary Masses from Multi-Transiting Exoplanetary Systems", The Astrophysical Journal, 762 (2): 112, arXiv:1211.4028v1, Bibcode:2013ApJ...762..112M, doi:10.1088/0004-637X/762/2/112, S2CID 29261765
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