Astronomy:Kepler-10

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Kepler-10, formerly known as KOI-72, is a Sun-like star in the constellation of Draco that lies 607 light-years (186 parsecs) from Earth.[1][2] Kepler-10 was targeted by NASA's Kepler space telescope, as it was seen as the first star identified by the Kepler mission that could be a possible host to a small, transiting exoplanet.[3] The star is slightly less massive, slightly larger, and slightly cooler than the Sun; at an estimated 11.9 billion years in age, Kepler-10 is 2.3 times the age of the Sun.[4]

Kepler-10 is host to a planetary system made up of at least three planets. Kepler-10b, the first undeniably rocky planet,[3] 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,[5] and has a density similar to that of iron.[3] 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 it was initially thought to have a higher density, making it the largest and most massive rocky planet discovered as of June 2014.[4][6][7] However, refined mass measurements have shown it to be a more typical volatile-rich planet.[8] A third planet, Kepler-10d, was discovered in 2023 by radial velocity observations.[9]

Nomenclature and history

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.[10] 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.[3] Although there had been many potentially rocky exoplanets discovered in the past, Kepler-10b was the first definitively rocky planet to have been discovered.[11]

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.[11] On May 23, 2011, the existence of Kepler-10c was confirmed at the 218th AAS meeting in Boston.[12]

Characteristics

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% less massive 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.[13] In addition, Kepler-10 is estimated to be 11.9 billion years old and to have an effective temperature of 5627 (± 44) K;[1] To compare, the Sun is younger and hotter, with an age of 4.6 billion years[14] and an effective temperature of 5778 K.[15]

Kepler-10 is located at a distance of 186 parsecs from the Earth, which equates to approximately 607 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.[1]

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

Planetary system

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 definitely 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+0.03−0.02 times that of Earth.[4] 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.[16] Because the planet orbits so closely to its star, its eccentricity is virtually zero. It, thus, has an extremely circular orbit.[5]

Kepler-10c[6] was also discovered by NASA's Kepler Mission,[17] the second exoplanet found to orbit Kepler-10. Radial-velocity measurements of the body initially suggested that it has a mass of 17.2±1.9 Earth masses and a radius of 2.35 Earth radii, which would have made 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.[4] However, in July 2017, more careful analysis of HARPS-N and HIRES data showed that Kepler-10c was much less massive than originally thought, instead around 7.37+1.32
−1.19 M⊕ with a mean density of 3.14 g/cm3. Instead of a primarily rocky composition, the more accurately determined mass of Kepler-10c suggests a world made almost entirely of volatiles, mainly water.[8]

A candidate third planet with an orbital period of about 102 days, given the provisional designation KOI-72.X, was identified in 2016 based on transit-timing variations.[18][8] In 2023, the presence of a third planet, Kepler-10d, was confirmed by radial velocity observations. It has an orbital period of 151 days and a minimum mass about 13 times that of Earth.[9]

The Kepler-10 planetary system[lower-alpha 1]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b 3.24±0.32 M⊕ 0.01685±0.00013 0.8374907±0.0000002 0 84.8+3.2
−3.9° 		1.470+0.030
−0.020 R⊕
c 11.29±1.24 M⊕ 0.2410±0.0019 45.294301±0.000048 0.121+0.035
−0.018 		89.623±0.011° 2.355±0.022 R⊕
d ≥13.00+0.73
−2.44 M⊕ 		0.5379±0.0044 151.09+0.18
−0.41 		0.190+0.027
−0.070 		— —

See also

Notes

  1. ↑ All masses, eccentricies, Kepler-10d's orbital period and Kepler-10c's inclination are from Bonomo et al. (2025),[19] the remaining from Bonomo et al. (2023).[19]

References

  1. ↑ 1.0 1.1 1.2 "Notes for star Kepler-10". Extrasolar Planets Encyclopaedia. 2011. http://www.exoplanet.eu/star.php?st=Kepler-10. Retrieved 13 March 2011. 
  2. ↑ "Kepler-10 Stellar Family Portrait". 22 May 2011. https://exoplanets.nasa.gov/resources/17/kepler-10-stellar-family-portrait/. 
  3. ↑ 3.0 3.1 3.2 3.3 "NASA'S Kepler Mission Discovers Its First Rocky Planet". Ames Research Center. NASA. 10 January 2011. http://www.kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=94. 
  4. ↑ 4.0 4.1 4.2 4.3 Dumusque, Xavier; Bonomo, Aldo S.; Haywood, Raphaëlle D.; Malavolta, Luca; Ségransan, Damien; Buchhave, Lars A.; Cameron, Andrew Collier; Latham, David W. 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. doi:10.1088/0004-637X/789/2/154. Bibcode: 2014ApJ...789..154D. 
  5. ↑ 5.0 5.1 "Summary Table of Kepler Discoveries". NASA. 2011. http://kepler.nasa.gov/Mission/discoveries/. 
  6. ↑ 6.0 6.1 Fressin, François et al. (2011). "Kepler-10c, A 2.2-Earth Radius Transiting Planet In A Multiple System". The Astrophysical Journal Supplement Series 197 (1): 5. doi:10.1088/0067-0049/197/1/5. Bibcode: 2011ApJS..197....5F. 
  7. ↑ Clavin, Whitney (June 2, 2014). "Astronomers Confounded By Massive Rocky World". NASA. http://www.jpl.nasa.gov/news/news.php?release=2014-171. 
  8. ↑ 8.0 8.1 8.2 Rajpaul, V. (July 2017), "Pinning down the mass of Kepler-10c: the importance of sampling and model comparison", Monthly Notices of the Royal Astronomical Society 471 (1): L25–L130, doi:10.1093/mnrasl/slx116, Bibcode: 2017MNRAS.471L.125R. 
  9. ↑ 9.0 9.1 Bonomo, A. S. et al. (April 2023). "Cold Jupiters and improved masses in 38 Kepler and K2 small-planet systems from 3661 high-precision HARPS-N radial velocities. No excess of cold Jupiters in small-planet systems". Astronomy & Astrophysics. doi:10.1051/0004-6361/202346211. 
  10. ↑ "Mission overview". Kepler and K2. NASA. 13 April 2015. https://www.nasa.gov/mission_pages/kepler/overview/index.html. 
  11. ↑ 11.0 11.1 Richard A. Lovett (10 January 2011). "NASA Finds Smallest Earthlike Planet Outside Solar System". National Geographic Society. http://news.nationalgeographic.com/news/2011/01/110110-nasa-kepler-10b-new-planet-found-rocky-science-space/. 
  12. ↑ "Kepler Spacecraft Shows That Smaller Planets Abound". Scientific American. 2011. https://www.scientificamerican.com/article.cfm?id=kepler-planet-census. 
  13. ↑ Henry Bortman (12 October 2004). "Extrasolar Planets: A Matter of Metallicity". Space Daily. https://www.spacedaily.com/news/extrasolar-04zl.html. 
  14. ↑ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. http://www.universetoday.com/18237/how-old-is-the-sun/. 
  15. ↑ Ed Grayzeck. "Sun Fact Sheet". Goddard Space Flight Center. NASA. http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html. 
  16. ↑ David Williams (17 November 2010). "Mercury Fact Sheet". Goddard Space Flight Center. NASA. http://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact.html. 
  17. ↑ "NASA'S Kepler Mission Discovers Its First Rocky Planet". NASA. 2011-01-10. http://www.nasa.gov/topics/universe/features/rocky_planet.html. 
  18. ↑ Weiss, Lauren M. et al. (March 2016). "Revised Masses and Densities of the Planets around Kepler-10". The Astrophysical Journal 819 (1): 83. doi:10.3847/0004-637X/819/1/83. Bibcode: 2016ApJ...819...83W. 
  19. ↑ 19.0 19.1 Bonomo, A. S.; Borsato, L.; Rajpaul, V. M.; Zeng, L.; Damasso, M.; Hara, N. C.; Cretignier, M.; Leleu, A. et al. (2025-02-11). "In-depth characterization of the Kepler-10 three-planet system with HARPS-N radial velocities and Kepler transit timing variations". Astronomy & Astrophysics 696: A233. doi:10.1051/0004-6361/202453026. Bibcode: 2025A&A...696A.233B. 

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



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