Kepler-20

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]

Kepler-20
Observation data
Epoch J2000      Equinox J2000
Constellation Lyra
Right ascension 19h 10m 47.5235s[1]
Declination +42° 20′ 19.299″[1]
Apparent magnitude (V) 12.51[2]
Characteristics
Spectral type G8[3]
Astrometry
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)
Details
Mass0.912±0.035[4] M☉
Radius0.944+0.06
−0.095[4] R☉
Temperature5466±93[4] K
Metallicity [Fe/H]0.02±0.04[4] dex
Age8.8+4.7
−2.7[4] Gyr
Other designations
KOI-070, KIC 6850504, 2MASS J19104752+4220194, Gaia DR2 2102548708017562112.[3]
Database references
SIMBADdata
KICdata

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
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 9.7+1.41
−1.44[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
−3.61[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

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. 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, arXiv:0807.2522, Bibcode:2008AJ....136..735L, doi:10.1088/0004-6256/136/2/735, S2CID 17641056
  3. "Kepler-20 -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg
  4. Schneider, Jean, "Star : Kepler-20", The Extrasolar Planets Encyclopaedia, CNRS/LUTH - Paris Observatory, archived from the original on 2012-01-19, retrieved 2011-12-21
  5. Johnson, Michele (20 December 2011). "NASA Discovers First Earth-size Planets Beyond Our Solar System". NASA. Retrieved 20 December 2011.
  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, archived from the original on 10 March 2012, retrieved 16 January 2012
  8. Fressin, Francois; et al. (February 2012). "Two Earth-sized planets orbiting Kepler-20". Nature. 482 (7384): 195–198. arXiv:1112.4550. Bibcode:2012Natur.482..195F. doi:10.1038/nature10780. PMID 22186831. S2CID 3182266.
  9. NASA Staff. "Artist's Concept of Kepler-20e". NASA. Retrieved 19 November 2014.
  10. http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=172
  11. Hand, Eric (20 December 2011). "Kepler discovers first Earth-sized exoplanets". Nature. doi:10.1038/nature.2011.9688. S2CID 122575277.
  12. Overbye, Dennis (20 December 2011). "Two Earth-Size Planets Are Discovered". New York Times. Retrieved 2011-12-21.
  13. Tate, Karl (20 December 2011). "At Last, Earth-Sized Alien Worlds (Infographic)". Space.com. Retrieved 2011-12-21.
  14. Fressin, Francois; et al. (20 December 2011). "Two Earth-sized planets orbiting Kepler-20". Nature. 482 (7384): 195–198. arXiv:1112.4550. Bibcode:2012Natur.482..195F. doi:10.1038/nature10780. PMID 22186831. S2CID 3182266.
  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, arXiv:1702.07714, doi:10.1093/mnras/stx461, S2CID 119325005
  16. 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. arXiv:1608.06836. Bibcode:2016AJ....152..160B. doi:10.3847/0004-6256/152/6/160. S2CID 216077870.

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