From HandWiki
Observation data
Equinox J2000.0]] (ICRS)
Constellation Lyra
Right ascension  19h 10m 47.5235s[1]
Declination +42° 20′ 19.299″[1]
Apparent magnitude (V) 12.51[2]
Spectral type G8V[3]
Proper motion (μ) RA: −3.976±0.039[1] mas/yr
Dec.: −26.959±0.043[1] mas/yr
Parallax (π)3.5103 ± 0.0219[1] mas
Distance929 ± 6 ly
(285 ± 2 pc)
Mass0.912±0.035[4] M
[4] R
Temperature5466±93[4] K
Metallicity [Fe/H]0.02±0.04[4] dex
[4] Gyr
Other designations
KOI-070, KIC 6850504, 2MASS J19104752+4220194, Gaia DR2 2102548708017562112.[3]
Database references

Kepler-20 is a star 929 light-years from Earth in the constellation Lyra with a system of six known planets.[5] The apparent magnitude of this star is 12.51, so it cannot be seen with the unaided eye. Viewing it requires a telescope with an aperture of 15 cm (6 in) or more.[6] It is slightly smaller than the Sun, with 94% of the Sun's radius and about 91% of the Sun's mass. The effective temperature of the photosphere is slightly cooler than that of the Sun at 5466 K, giving it the characteristic yellow hue of a stellar class G8 star.[7][8] The abundance of elements other than hydrogen or helium, what astronomers term the metallicity, is approximately the same as in the Sun. It may be older than the Sun, although the margin of error here is relatively large.[4]

Planetary system

Size comparison of Kepler-20e and Kepler-20f (artist's impressions) with Venus and Earth (actual photographs)

On December 20, 2011, the Kepler Space Telescope team reported the discovery of a five-planet system containing three small gas giants and the first two Earth-sized extrasolar planets, Kepler-20e (the first known extrasolar planet smaller than Earth orbiting a main-sequence star)[9] and Kepler-20f, orbiting a Sun-like star.[10] Although the planets are Earth-sized, they are not Earth-like in the respect that they are much closer to their star than Earth, and are hence not near the habitable zone,[11] with expected surface temperatures of 760 °C (1,400 °F) and 427 °C (801 °F), respectively. The three other Neptune-sized planets in the system, Kepler-20b, Kepler-20c, and Kepler-20d, all orbit similarly close to the star.[12][13] Kepler-20g is a non-transiting Neptunian world.

The masses of e and f are expected masses. Their masses are uncertain as they are too small to detect via radial velocity with current technology.[14]

All planets are at small near resonances; proceeding outwards, they are 3:2, 4:2, 2:1, 4:1. The planetary orbits in current form are highly sensitive to perturbations caused by outer planets, therefore assuming stability, no additional gas giant planets can be located closer than 30 AU from the parent star.[15]

The Kepler-20 planetary system
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 9.7+1.41
[16] M
0.04537 +0.00054−0.00060 3.6961219 <0.32 1.91 R
e 0.39–1.67 M 0.0630 6.098493 <0.28 0.868 R
c 16.1 M 0.0930± 0.0011 10.854092 <0.40 3.07 R
f 0.66–3.04 M 0.1370 19.57706 <0.32 1.034 R
g 19.96+3.08
[16] M
0.2055 34.940 ≤ 0.16
d <20.1 M 0.3453 +0.0041−0.0046 77.61184 <0.60 2.75 R

See also


  1. 1.0 1.1 1.2 1.3 1.4 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  2. Lasker, Barry M. et al. (August 2008), "The Second-Generation Guide Star Catalog: Description and Properties", The Astronomical Journal 136 (2): 735–766, doi:10.1088/0004-6256/136/2/735, Bibcode2008AJ....136..735L 
  3. 3.0 3.1 "Kepler-20 -- Star", SIMBAD (Centre de Données astronomiques de Strasbourg), 
  4. 4.0 4.1 4.2 4.3 4.4 4.5 Schneider, Jean, Star : Kepler-20, CNRS/LUTH - Paris Observatory,, retrieved 2011-12-21 
  5. Johnson, Michele (20 December 2011). "NASA Discovers First Earth-size Planets Beyond Our Solar System". NASA. 
  6. Sherrod, P. Clay; Koed, Thomas L. (2003), A Complete Manual of Amateur Astronomy: Tools and Techniques for Astronomical Observations, Astronomy Series, Courier Dover Publications, p. 9, ISBN 0-486-42820-6, 
  7. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004,, retrieved 16 January 2012 
  8. Fressin, Francois et al. (February 2012). "Two Earth-sized planets orbiting Kepler-20". Nature 482 (7384): 195–198. doi:10.1038/nature10780. PMID 22186831. Bibcode2012Natur.482..195F. 
  9. NASA Staff. "Artist's Concept of Kepler-20e". NASA. 
  11. Hand, Eric (20 December 2011). "Kepler discovers first Earth-sized exoplanets". Nature. doi:10.1038/nature.2011.9688. 
  12. Overbye, Dennis (20 December 2011). "Two Earth-Size Planets Are Discovered". New York Times. 
  13. Tate, Karl (20 December 2011). "At Last, Earth-Sized Alien Worlds (Infographic)". 
  14. Fressin, Francois et al. (20 December 2011). "Two Earth-sized planets orbiting Kepler-20". Nature 482 (7384): 195–198. doi:10.1038/nature10780. PMID 22186831. Bibcode2012Natur.482..195F. 
  15. Becker, Juliette C.; Adams, Fred C. (2017), "Effects of Unseen Additional Planetary Perturbers on Compact Extrasolar Planetary Systems", Monthly Notices of the Royal Astronomical Society 468: 549–563, doi:10.1093/mnras/stx461 
  16. 16.0 16.1 Buchhave, Lars A. et al. (14 November 2016). "A 1.9 Earth radius rocky planet and the discovery of a non-transiting planet in the Kepler-20 system". The Astronomical Journal 152 (6): 160. doi:10.3847/0004-6256/152/6/160. Bibcode2016AJ....152..160B. 

External links

Coordinates: Sky map 19h 10m 47.5s, +42° 20′ 19.4″