Kepler-20

Kepler-20

Kepler-20 planets, Kepler-20e[1] and Kepler-20f,[2] in comparison with Venus and Earth.
Observation data
Epoch J2000      Equinox J2000
Constellation Lyra
Right ascension 19h 10m 47.524s[3]
Declination +42° 20′ 19.30″[3]
Apparent magnitude (V) 12.51[4]
Characteristics
Spectral type G8[5]
Astrometry
Proper motion (μ) RA: –4.2[3] mas/yr
Dec.: –26.3[3] mas/yr
Distance ca. 950 ly
(290 ± 30[6] pc)
Details
Mass 0.912 ± 0.035[6] M☉
Radius 0.944+0.06
−0.095[6] R☉
Temperature 5,466 ± 93[6] K
Metallicity [Fe/H] 0.02 ± 0.04[6] dex
Age 8.8+4.7
−2.7[6] Gyr
Other designations
KOI-070, KIC-6850504, 2MASS J19104752+4220194.[5]

Kepler-20 is a star 950 light-years from Earth[7] in the constellation Lyra with a system of five known planets.[8] The apparent magnitude of this star is 12.51, so it cannot be seen with the unaided eye. Viewing it would require a telescope with an aperture of 15 cm (6 in) or more.[9] 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 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.[6]

Contents

Planetary system

On December 20, 2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets, Kepler-20e[1] and Kepler-20f,[2] orbiting a Sun-like star.[7][8] While the planets are Earth-sized, they are not Earth-like in other important respects: they are "nowhere near a habitable zone" according to the NASA report,[7] with expected surface temperatures of 760 °C (1,400 °F) and 427 °C (801 °F), respectively. Both planets have orbits smaller than that of Mercury.[10] Three other Neptune-sized planets have been observed in the system, designated Kepler-20b, Kepler-20c, and Kepler-20d. The order of the planets within the system, by their distance from the sun, is b-e-c-f-d. All orbit within the equivalent of Mercury's orbit around the Sun.[11][12]

This planetary system is unlike our own, with the orbits of gas giants alternating with those of terrestrial-mass planets.

See also

References

  1. ^ a b NASA Staff (20 December 2011). "Kepler: A Search For Habitable Planets - Kepler-20e". NASA. http://kepler.nasa.gov/Mission/discoveries/kepler20e/. Retrieved 2011-12-23. 
  2. ^ a b NASA Staff (20 December 2011). "Kepler: A Search For Habitable Planets - Kepler-20f". NASA. http://kepler.nasa.gov/Mission/discoveries/kepler20f/. Retrieved 2011-12-23. 
  3. ^ a b c d Zacharias, N. et al. (June 2010), "The Third US Naval Observatory CCD Astrograph Catalog (UCAC3)", The Astronomical Journal 139 (6): 2184-2199, Bibcode 2010AJ....139.2184Z, doi:10.1088/0004-6256/139/6/2184  See the online data VizieR results for 3UC 265-159969.
  4. ^ Lasker, Barry M. et al. (August 2008), "The Second-Generation Guide Star Catalog: Description and Properties", The Astronomical Journal 136 (2): 735–766, Bibcode 2008AJ....136..735L, doi:10.1088/0004-6256/136/2/735 
  5. ^ a b "Kepler-20 -- Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Kepler-20 
  6. ^ a b c d e f g Schneider, Jean, "Star : Kepler-20", The Extrasolar Planets Encyclopaedia (CNRS/LUTH - Paris Observatory), http://exoplanet.eu/star.php?st=Kepler-20, retrieved 2011-12-21 
  7. ^ a b c Hand, Eric (20 December 2011). "Kepler discovers first Earth-sized exoplanets". Nature. doi:10.1038/nature.2011.9688. 
  8. ^ a b Johnson, Michele (20 December 2011). "NASA Discovers First Earth-size Planets Beyond Our Solar System". NASA. http://www.nasa.gov/mission_pages/kepler/news/kepler-20-system.html. Retrieved 2011-12-20. 
  9. ^ Sherrod, P. Clay; Koed, Thomas L. (2003), A Complete Manual of Amateur Astronomy: Tools and Techniques for Astronomical Observations, Courier Dover Publications, p. 9, ISBN 0486428206, http://books.google.com/books?id=4zjv84hHNPcC&pg=PA9 
  10. ^ Moskowitz, Clara (20 December 2011). "First Ever 'Earth-Sized' Alien Planets Discovered". Fox News Channel. http://www.foxnews.com/scitech/2011/12/20/first-ever-earth-sized-alien-planets-discovered/. Retrieved 2011-12-20. 
  11. ^ Overbye, Dennis (20 December 2011). "Two Earth-Size Planets Are Discovered". New York Times. http://www.nytimes.com/2011/12/21/science/space/nasas-kepler-spacecraft-discovers-2-earth-size-planets.html. Retrieved 2011-12-21. 
  12. ^ Tate, Karl (20 December 2011). "At Last, Earth-Sized Alien Worlds (Infographic)". Space.com. http://www.space.com/13987-earth-size-alien-planets-kepler-22e-infographic.html. Retrieved 2011-12-21. 

External links