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Observation data
Epoch J2000      Equinox J2000
Constellation Lyra
Right ascension 18h 45m 09.1490s[1]
Declination +42° 27′ 03.892″[1]
Apparent magnitude (V) 13.9
Spectral type F5V
Proper motion (μ) RA: 2.196±0.023[1] mas/yr
Dec.: 3.841±0.027[1] mas/yr
Parallax (π) 0.9498 ± 0.0139[1] mas
Distance 3,430 ± 50 ly
(1,050 ± 20 pc)
Mass 1.213 M
Radius 1.486 R
Temperature 6213 K
Age 3.84 Gyr
Other designations
KIC 6922244, KOI-10
Database references
KIC data

Kepler-8 is a star located in the constellation Lyra in the field of view of the Kepler Mission, a NASA-led operation tasked with discovering terrestrial planets. The star, which is slightly hotter, larger, and more massive than the Sun, has one gas giant in its orbit, Kepler-8b. This gas giant is larger than Jupiter, but is less massive, and thus more diffuse. The planet's discovery was announced to the public on January 4, 2010 along with four other planets. As the fifth confirmed planetary system verified by Kepler, it helped demonstrate the capabilities of the Kepler spacecraft.

Nomenclature and history[edit]

Kepler-8 was named the way it was because it is home to the eighth planetary system confirmed during the course of the Kepler Mission, a NASA-directed program tasked with searching a region of the sky for terrestrial planets that transit, or cross in front of (and thereby, for a while, make dimmer) the stars that they orbit with respect to Earth.[2] The planet in orbit around Kepler-8, Kepler-8b, was the fifth of the first five planets discovered by the Kepler spacecraft; the first three planets confirmed by Kepler had been previously discovered, and were only used to verify the accuracy of Kepler's measurements.[3] Kepler-8b's discovery was announced to the public on January 4, 2010 at the 215th meeting of the American Astronomical Society in Washington, D.C., alongside planets in orbit around Kepler-4, Kepler-5, Kepler-6, and Kepler-7.[4]

The data that was used to identify Kepler-8b's existence was re-examined and verified by observatories in Hawaii, Arizona, Texas, California, and the Canary Islands.[5]


Kepler-8 is situated some 1050 pc (or 3,400 light years) from Earth.[1] With a mass of 1.213 Msun and a radius of 1.486 Rsun, Kepler-8 is more massive than the Sun by about a fifth of the Sun's mass, and is nearly three halves its size. The star is predicted to be 3.84 (± 1.5) billion years old, compared to the Sun's age at 4.6 billion years.[6] Kepler-8 has a metallicity of [Fe/H] = -0.055 (± 0.03), making it 12% less metal-rich than the metal-rich Sun; metallicity is important in stars because stars richer in metal are more likely to harbor planets.[7] The star also has an effective temperature of 6213 (± 150) K, meaning that it is hotter than the Sun, which has an effective temperature of 5778 K.[8][9]

The first five planets discovered by Kepler, compared by relative size. Kepler-8b is depicted in orange.

Kepler-8 has an apparent magnitude of 13.9; in other words, as seen from Earth, Kepler-8 is an extremely dim star. It cannot be seen with the naked eye.[9]

Planetary system[edit]

Kepler-8b is the only planet that has been discovered in the orbit of Kepler-8. With a mass of .603 MJ and a radius of 1.419 RJ, the planet is 60% the mass of, but 42% larger than planet Jupiter. The planet is diffuse, with a density of .261 grams/cc, especially in comparison to Jupiter and its density of 5.515 grams/cc. At a distance of .0483 AU, Kepler-8b orbits its star every 3.5225 days. The eccentricity of Kepler-8 is assumed to be 0, which would give the planet a circular orbit.[3] In comparison, planet Mercury orbits the Sun at .3871 AU every 87.97 days. Mercury also has an elliptical orbit, with an eccentricity of .2056.[10]

The Kepler-8 planetary system[3]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 0.603 MJ 0.0483 3.5225 0 1.419 RJ

See also[edit]


  1. ^ a b c d e f Brown, A. G. A.; Vallenari, A.; Prusti, T.; de Bruijne, J. H. J.; et al. (Gaia Collaboration) (April 2018). "Gaia Data Release 2. Summary of the contents and survey properties". Astronomy & Astrophysics. arXiv:1804.09365Freely accessible. Bibcode:2018arXiv180409365G. doi:10.1051/0004-6361/201833051.  Gaia Data Release 2 catalog entry
  2. ^ "Kepler: About the Mission". Kepler Mission. NASA. 2011. Retrieved 27 February 2011. 
  3. ^ a b c "Summary Table of Kepler Discoveries". NASA. 2010-08-27. Retrieved 2010-10-16. 
  4. ^ Rich Talcott (5 January 2010). "215th AAS meeting update: Kepler discoveries the talk of the town". Astronomy magazine. Retrieved 27 February 2011. 
  5. ^ "NASA's Kepler Space Telescope Discovers its FIrst Five Exoplanets". NASA. 4 January 2010. Retrieved 27 February 2011. 
  6. ^ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 27 February 2011. 
  7. ^ Henry Bortman (12 October 2004). "Extrasolar Planets: A Matter of Metallicity". Space Daily. Retrieved 27 February 2011. 
  8. ^ David Williams (1 September 2004). "Sun Fact Sheet". Goddard Space Flight Center. NASA. Retrieved 27 February 2011. 
  9. ^ a b "Notes for star Kepler-8". Extrasolar Planets Encyclopaedia. 2010. Archived from the original on 21 January 2011. Retrieved 27 February 2011. 
  10. ^ David Williams (17 November 2010). "Mercury Fact Sheet". Goddard Space Flight Center. NASA. Retrieved 27 February 2011. 

Coordinates: Sky map 18h 45m 9.1s, +42° 27′ 3.8″