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An artist's depiction of the Kepler-10 system. Kepler-10c is in the foreground.
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension 19h 02m 43s
Declination +50° 14′ 29″
Apparent magnitude (V) 11.157[1]
Distance 564 ly
(173[2] pc)
Spectral type G[2]
Mass 0.910±0.021[1] M
Radius 1.065±0.009[1] R
Temperature 5708±28[1] K
Age 10.6+1.5
[1] Gyr
Other designations
KOI 72,[3] KIC 11904151,[4] GSC 03549-00354,[3] 2MASS J19024305+5014286[3]

Kepler-10, formerly known as KOI-72, is a Sun-like star in the constellation of Draco that lies 173 parsecs (564 light years) from Earth. Kepler-10 was targeted by NASA's Kepler spacecraft, as it was seen as the first star identified by the Kepler mission that could be a possible host to a small, transiting exoplanet.[5] The star is slightly less massive, slightly larger, and slightly cooler than the Sun; at an estimated 10.4 billion years in age, Kepler-10 is almost 2.6 times the age of the Sun. Kepler-10 is host to a planetary system made up of at least two planets. Kepler-10b, the first undeniably rocky planet,[5] was discovered in its orbit after eight months of observation and announced on January 10, 2011. The planet orbits its star closely, completing an orbit every 0.8 days,[6] and has a density similar to that of iron.[5] The second planet, Kepler-10c, was confirmed on May 23, 2011, based on follow-up observations by the Spitzer Space Telescope. The data shows it has an orbital period of 42.3 days and has a radius more than double that of Earth, but a higher density, making it the largest and most massive rocky planet discovered as of June 2014.[1][7][8]

Nomenclature and history[edit]

Kepler-10 was named because it was the tenth planetary system observed by the Kepler spacecraft, a NASA satellite designed to search for Earth-like planets that transit, or cross in front of, their host stars with respect to Earth. The transit slightly dims the host star; this periodic dimming effect is then noted by Kepler.[9] After eight months of observation ranging from May 2009 to January 2010, the Kepler team established Kepler-10b as the first rocky exoplanet discovered by the Kepler satellite. Kepler-10 was the first Kepler-targeted star suspected of having a small planet in orbit. Because of that, verifying Kepler's discovery was prioritized by telescopes at the W.M. Keck Observatory in Hawaii. The discovery was successfully verified.[5] Although there had been many potentially rocky exoplanets discovered in the past, Kepler-10b was the first definitively rocky planet to have been discovered.[10]

The discovery of Kepler-10b was announced to the public at a winter meeting of the American Astronomical Society on January 10, 2011 in Seattle.[10] On May 23, 2011, the existence of Kepler-10c was confirmed at the 218th AAS meeting in Boston.[11]


Kepler-10 is a G-type star, like the Sun. With a mass of 0.895 (± 0.06) Msun and a radius of 1.056 (± 0.021) Rsun, the star is approximately 10% smaller than and 5% wider than the Sun. The metallicity of Kepler-10, as measured in [Fe/H] (the amount of iron in the star), is -0.15 (± 0.04); this means that Kepler-10 is about 70% as metal-rich as the Sun. Metallicity tends to play a large role in the formation of planets, determining if they form, and what kind of planet they will form.[12] In addition, Kepler-10 is estimated to be 11.9 billion years old and to have an effective temperature of 5627 (± 44) K;[2] To compare, the Sun is younger and hotter, with an age of 4.6 billion years[13] and an effective temperature of 5778 K.[14]

Kepler-10 is located at a distance of 173 (± 27) parsecs from the Earth, which equates to approximately 564 light years. Also, Kepler-10's apparent magnitude, or brightness as seen from Earth, is 10.96; it therefore cannot be seen with the naked eye.[2]

An artist's impression of planet Kepler-10b.

Planetary system[edit]

Per the usual exoplanet nomenclature, the first planet discovered to be orbiting Kepler-10 is called Kepler-10b. Announced in 2011, it was the first rocky planet identified outside the Solar system. The planet has a mass that is 3.33±0.49 times that of Earth's and a radius that is 1.47+0.03
times that of Earth.[1] The planet orbits Kepler-10 at a distance of 0.01684 AU every 0.8375 days; this can be compared to the orbit and orbital period of planet Mercury, which circles the Sun at a distance of 0.3871 AU every 87.97 days.[15] Because the planet orbits so closely to its star, its eccentricity is virtually zero. It, thus, has an extremely circular orbit.[6]

Kepler-10c[7] was also discovered by NASA's Kepler Mission,[16] the second exoplanet found to orbit Kepler-10. Radial-velocity measurements of the body suggest that it has a mass of 17.2±1.9 Earth masses and a radius of 2.35 Earth radii, making it the largest known rocky planet as of 2014. Kepler-10c would orbit Kepler-10 at a distance of 0.24 AU every 45.29 days.[1]

The Kepler-10 planetary system[6]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 3.33±0.49 M 0.01684 0.837495 0 84.8+3.2
c 17.2±1.9 M 0.2410 45.29485 0 89.59+0.25
Kepler-10 System.

See also[edit]


  1. ^ a b c d e f g h Dumusque, Xavier; Bonomo, Aldo S.; Haywood, Raphaëlle D.; Malavolta, Luca; Ségransan, Damien; Buchhave, Lars A.; Cameron, Andrew Collier; Latham, David W.; Molinari, Emilio; Pepe, Francesco; Udry, Stéphane; Charbonneau, David; Cosentino, Rosario; Dressing, Courtney D.; Figueira, Pedro; Fiorenzano, Aldo F. M.; Gettel, Sara; Harutyunyan, Avet; Horne, Keith; Lopez-Morales, Mercedes; Lovis, Christophe; Mayor, Michel; Micela, Giusi; Motalebi, Fatemeh; Nascimbeni, Valerio; Phillips, David F.; Piotto, Giampaolo; Pollacco, Don; Queloz, Didier; et al. (2014). "The Kepler-10 Planetary System Revisited by Harps-N: A Hot Rocky World and a Solid Neptune-Mass Planet". The Astrophysical Journal. 789 (2): 154. arXiv:1405.7881free to read. Bibcode:2014ApJ...789..154D. doi:10.1088/0004-637X/789/2/154. 
  2. ^ a b c d "Notes for star Kepler-10". Extrasolar Planets Encyclopaedia. 2011. Retrieved 13 March 2011. 
  3. ^ a b c "Kepler-10 -- Star". SIMBAD. Retrieved 2011-02-01. 
  4. ^ Batalha, N. M.; et al. (2011). "Kepler's First Rocky Planet: Kepler-10b". The Astrophysical Journal. 729: 27. arXiv:1102.0605free to read. Bibcode:2011ApJ...729...27B. doi:10.1088/0004-637X/729/1/27. 
  5. ^ a b c d Perrotto, Trent J.; Hoover, Rachel (10 January 2011). "NASA'S Kepler Mission Discovers Its First Rocky Planet". Ames Research Center. NASA. Retrieved 13 March 2011. 
  6. ^ a b c "Summary Table of Kepler Discoveries". NASA. 2011. Retrieved 13 March 2011. 
  7. ^ a b Fressin, F.; et al. (2011). "Kepler-10c, A 2.2-Earth Radius Transiting Planet In A Multiple System". arXiv:1105.4647free to read [astro-ph.EP]. 
  8. ^ Clavin, Whitney (June 2, 2014). "Astronomers Confounded By Massive Rocky World". NASA. Retrieved June 3, 2014. 
  9. ^ "Kepler: About the Mission". Kepler Mission. NASA. 2011. Retrieved 13 March 2011. 
  10. ^ a b Richard A. Lovett (10 January 2011). "NASA Finds Smallest Earthlike Planet Outside Solar System". National Geographic Society. Retrieved 13 March 2011. 
  11. ^ "Kepler Spacecraft Shows That Smaller Planets Abound". Scientific American. 2011. Retrieved 2011-05-26. 
  12. ^ Henry Bortman (12 October 2004). "Extrasolar Planets: A Matter of Metallicity". Space Daily. Retrieved 13 March 2011. 
  13. ^ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 13 March 2011. 
  14. ^ Ed Grayzeck. "Sun Fact Sheet". Goddard Space Flight Center. NASA. Retrieved 13 March 2011. 
  15. ^ David Williams (17 November 2010). "Mercury Fact Sheet". Goddard Space Flight Center. NASA. Retrieved 27 February 2011. 
  16. ^ "NASA'S Kepler Mission Discovers Its First Rocky Planet". NASA. 2011-01-10. Retrieved 2011-01-10. 

Coordinates: Sky map 19h 02m 43s, +50° 14′ 28.7″