Epoch J2000 Equinox J2000
|Right ascension||19h 10m 47.524s|
|Declination||+42° 20′ 19.30″|
|Apparent magnitude (V)||12.51|
|Proper motion (μ)||RA: –4.2 mas/yr
Dec.: –26.3 mas/yr
|Distance||ca. 950 ly
(290 ± 30 pc)
|Mass||0.912 ± 0.035 M☉|
|Temperature||5,466 ± 93 K|
|Metallicity [Fe/H]||0.02 ± 0.04 dex|
Kepler-20 is a star 950 light-years from Earth in the constellation Lyra with a system of five known planets. 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. 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 5,466 K, giving it the characteristic yellow hue of a stellar class G8 star. As of 2011, it has not yet been determined whether this is a main-sequence star. 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.
On December 20, 2011, the Kepler Space Telescope team reported the discovery of a five planet system containing three small gas giant planets and the first two Earth-sized extrasolar planets, Kepler-20e (the first known extrasolar planet smaller than Earth orbiting a main-sequence star)[not in citation given][contradictory] and Kepler-20f, orbiting a Sun-like star. 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, 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.
The masses of e and f are uncertain as they are expected masses; their masses are too small to detect via radial velocity with current technology.
All planets are at small near resonances; proceeding outwards, they are 3:2, 4:2, 2:1, 4:1.
(in order from star)
|b||8.7 M⊕||0.04537||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||10.854092||<0.40||—||3.07 R⊕|
|f||0.66–3.04 M⊕||0.1370||19.57706||<0.32||—||1.034 R⊕|
|d||<20.1 M⊕||0.3453||77.61184||<0.60||—||2.75 R⊕|
- Zacharias, N. et al. (June 2010), "The Third US Naval Observatory CCD Astrograph Catalog (UCAC3)", The Astronomical Journal 139 (6): 2184–2199, arXiv:1003.2136, Bibcode:2010AJ....139.2184Z, doi:10.1088/0004-6256/139/6/2184 See the online data VizieR results for 3UC 265-159969.
- 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
- "Kepler-20 -- Star", SIMBAD (Centre de Données astronomiques de Strasbourg)
- Schneider, Jean, "Star : Kepler-20", The Extrasolar Planets Encyclopaedia (CNRS/LUTH - Paris Observatory), retrieved 2011-12-21
- Hand, Eric (20 December 2011). "Kepler discovers first Earth-sized exoplanets". Nature. doi:10.1038/nature.2011.9688.
- Johnson, Michele (20 December 2011). "NASA Discovers First Earth-size Planets Beyond Our Solar System". NASA. Retrieved 2011-12-20.
- 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
- "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
- NASA Staff (20 December 2011). "Kepler: A Search For Habitable Planets - Kepler-20e". NASA. Retrieved 2011-12-23.
- NASA Staff (20 December 2011). "Kepler: A Search For Habitable Planets - Kepler-20f". NASA. Retrieved 2011-12-23.
- Overbye, Dennis (20 December 2011). "Two Earth-Size Planets Are Discovered". New York Times. Retrieved 2011-12-21.
- Tate, Karl (20 December 2011). "At Last, Earth-Sized Alien Worlds (Infographic)". Space.com. Retrieved 2011-12-21.
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