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Exoplanet List of exoplanets
Kepler-20f Planet.jpg
An artist's depiction of Kepler-20f.
Parent star
Star Kepler-20 (KOI-070)
Constellation Lyra
Right ascension (α) 19h 10m 47.524s
Declination (δ) +42° 20′ 19.30″
Apparent magnitude (mV) 12.51
Distance 950 ly
(290±30 pc)
Spectral type G8V
Mass (m) 0.912±0.035[1] M
Radius (r) 0.944+0.06
[1] R
Temperature (T) 5466±93[1] K
Metallicity [Fe/H] 0.02±0.04[1]
Age 8.8+4.7
[1] Gyr
Physical characteristics
Mass (m) ~1 M
Radius (r) 1.003+0.050
Stellar flux (F) 59
Temperature (T) 705 K (432 °C; 809 °F)
Orbital elements
Semi-major axis (a) 0.1104 AU
Eccentricity (e) <0.32
Orbital period (P) 19.57706 d
Inclination (i) 88.68+0.17
Discovery information
Discovery date 20 December 2011
Discoverer(s) Kepler team
Discovery method Transit (Kepler Mission)
Discovery status Conference announcement
Other designations
2MASS J19104752+4220194 f, KOI-70.05, KOI-70 f, KIC 6850504 f
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

Kepler-20f (also known by its Kepler Object of Interest designation KOI-70.05) is an exoplanet orbiting the Sun-like star Kepler-20, the second outermost of five such planets discovered by NASA's Kepler spacecraft. It is located approximately 950 light-years (290 parsecs, or about 8.988×1015 km) from Earth in the constellation Lyra. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured. The planet is notable as it has the closest radius to Earth known so far.


Kepler-20e and Kepler-20f compared to Venus and Earth

Mass, radius and temperature[edit]

Kepler-20f is very likely (>95% chance) a rocky planet because of its radius, which is notable as being the closet to Earth yet: 1.004 R.[2] However, although its radius is almost the same as Earth's, its surface conditions are not Earth-like in any way. The equilibrium temperature of Kepler-20f is approximately 705 K (432 °C; 809 °F), too hot to support liquid water on its surface and hot enough to melt some types of metal.[2] But because of its size, it can be expected to have an atmosphere of water vapor. The mass of the planet can be approximated to around 0.66–3.04 M, depending on its composition. An Earth-like composition would have its mass to be around 1.2 M.

Host star[edit]

Kepler-20 is a Sun-like star in the constellation Lyra with a mass of 0.91 (± 0.03) M and a radius of 0.94 (± 0.06) R, and is thought to be 8.8 billion years old, though there is a large uncertainty in its age.[1] In other words, Kepler-20 is approximately 9% less massive and 6% shorter than the Sun. The star's metallicity is 0.01 (± 0.04), meaning that the level of iron (and, presumably, other elements) in the star is almost the same as that of the Sun.[1] Metallicity plays an important role in planetary systems, and stars with higher metallicity are more likely to have planets detected around them.[3] This may be because the higher metallicity provides more material with which to quickly build planets into gas giants or because the higher metallicity increases planet migration towards the host star, making the planet easier to detect.[4] The star has four other known planets in orbit: Kepler-20b, Kepler-20c, Kepler-20d, and Kepler-20e. All of the planets in the system would fit inside the orbit of Mercury.

Kepler-20 has an apparent magnitude of 12.51, too dim to be seen from Earth with the naked eye.


With a semimajor axis of 0.1104 AU, Kepler-20f's orbit has a period of 19.57706 days (with an extremely small margin of error). The planet also has an inclination of 88.68°, which of course makes its transits observable from the Solar System. Like the other planets of the system, the planet has a high maximum eccentricity of 0.32. The planet is also in a 4:1 near resonance with Kepler-20c.


In 2009, NASA's Kepler spacecraft was completing observing stars on its photometer, the instrument it uses to detect transit events, in which a planet crosses in front of and dims its host star for a brief and roughly regular period of time. In this last test, Kepler observed 50000 stars in the Kepler Input Catalog, including Kepler-20; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up at observatories. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. After observing the respective transits, which for Kepler-20f occurred roughly every 19 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 19-day transits. The exoplanet, along with the other planets of the Kepler-20 system and other planets around stars studied by Kepler, were announced on December 20, 2011.[2]


  1. ^ a b c d e f g Schneider, Jean, "Star : Kepler-20", The Extrasolar Planets Encyclopaedia, CNRS/LUTH - Paris Observatory, retrieved 2011-12-21 
  2. ^ a b c "NASA Discovers First Earth-size Planets Beyond Our Solar System". NASA. 20 December 2011. Retrieved 19 June 2016. 
  3. ^ Fischer, Debra A.; Valenti,Jeff (2005-04-01). "The planet-metallicity correlation". The Astrophysical Journal. 622 (2): 1102–1117. Bibcode:2005ApJ...622.1102F. doi:10.1086/428383. Retrieved 2011-03-27. 
  4. ^ Seager, Sara (2010). "Statistical Distribution of Exoplanets by Andrew Cumming". Exoplanets. University of Arizona Press. pp. 191–214. ISBN 978-0-8165-2945-2. 

See also[edit]

  • Kepler-20e – another exoplanet in the Kepler-20 system, with a radius slightly smaller than that of Earth.

Coordinates: Sky map 19h 10m 47.524s, +42° 20′ 19.30″