Epoch J2000 Equinox J2000
|Right ascension||19h 48m 27.622s|
|Declination||+41° 54′ 32.87″|
|Apparent magnitude (V)||14.2|
|Proper motion (μ)||RA: –0.7 mas/yr
Dec.: –4.1 mas/yr
|Mass||0.95 (± 0.1) M☉|
|Radius||1.1 (± 0.1) R☉|
|Surface gravity (log g)||4.47|
|Temperature||5680 (± 100) K|
|Metallicity [Fe/H]||0 (± 0.1) dex|
|Age||8 (± 2) Gyr|
Kepler-11 is a sun-like star slightly larger than the Sun in the constellation Cygnus, located some 2,000 light years from Earth. It is located within the field of vision of the Kepler spacecraft, the satellite that NASA's Kepler Mission uses to detect planets that may be transiting their stars. Announced on February 2, 2011, the star system is among the most compact and flattest systems yet discovered. It is the first discovered case of a star system with six transiting planets. All discovered planets are larger than Earth, with the larger ones being about Neptune's size.
Nomenclature and history 
Kepler-11 and its planets were discovered by NASA's Kepler Mission, a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits move in front of their stars from the perspective of Earth. Kepler-11 is the first discovered exoplanetary system with more than three transiting planets.
Kepler-11 is named for the Kepler Mission: it is the 11th star with confirmed planets discovered by Kepler. The planets are named alphabetically, starting with the innermost: b, c, d, e, f, and g, distinguishers that are tagged onto the name of their home star.
Kepler-11 is a G-type star that is approximately 95% the mass of and 110% the radius of the Sun. It has a surface temperature of 5680 (± 100) K and is 8 (± 2) billion years old. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K.
Planetary system 
All known planets transit the star; this means that all six planets' orbits appear to cross in front of their star as viewed from the Earth's perspective. Their inclinations relative to Earth's line of sight, or how far above or below the plane of sight they are, vary by a little more than a degree. This allows direct measurements of the planets' periods and relative diameters (compared to the host star) by monitoring each planet's transit of the star. Simulations suggest that the mean mutual inclinations of the planetary orbits are about 1°, meaning the system is probably more coplanar (flatter) than the Solar System, where the corresponding figure is 2.3°.
The estimated masses of planets b - f fall in the range between those of Earth and Neptune. Their estimated densities, all lower than that of Earth, imply that none of them have an Earth-like composition; a significant hydrogen atmosphere is indicated for planets d, e and perhaps f, while b and c probably contain substantial amounts of ices and either hydrogen and helium or both. The low densities likely result from high-volume extended atmospheres that surround cores of iron, rock, or both. The inner constituents of the Kepler-11 system were, at the time of their discoveries, the most comprehensively understood extrasolar planets smaller than Neptune.
The system is among the most compact known; the orbits of planets b - f would easily fit inside the orbit of Mercury, with g only slightly outside it. Despite this close packing of the orbits, dynamical integrations indicate the system has the potential to be stable on a time scale of billions of years.
None of the planets are in low-ratio orbital resonances, in which multiple planets gravitationally tug on and stabilize each other's orbits, resulting in simple ratios of their orbital periods. However, b and c are close to a 5:4 ratio.
There could conceivably be other planets in the system that do not transit the star, but they would only be detectable by the effects of their gravity on the motion of the visible planets (much as how Neptune was discovered).
|b||4.3 (2.3 - 6.5)||1.97 ± 0.19||3.1 (1.6 - 5.2)||10.30375||0.091||0||88.5||2011|
|c||13.5 (7.4 - 18.3)||3.15 ± 0.30||2.3 (1.2 - 3.6)||13.02502||0.106||0||89||2011|
|d||6.1 (4.4 - 9.2)||3.43 ± 0.32||0.9 (0.6 - 1.4)||22.68719||0.159||0||89.3||2011|
|e||8.4 (6.5 - 10.9)||4.52 ± 0.43||0.5 (0.3 - 0.7)||31.9959||0.194||0||88.8||2011|
|f||2.3 (1.1 - 4.5)||2.61 ± 0.25||0.7 (0.3 - 1.4)||46.68876||0.25||0||89.4||2011|
|g||<300||3.66 ± 0.35||Unknown||118.37774||0.462||0||89.8||2011|
Relative size and positions of the 6 planets of Kepler-11, and of the innermost Solar System for comparison.
The diameters of the planets (but not of the stars!) are scaled up by a factor of 50 times larger than actual scale.
See also 
- 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.
- "Kepler Discoveries". NASA Ames Research Center. Retrieved 4 February 2011.
- Lissauer, J. J.; et al. (3 February 2011). "A closely packed system of low-mass, low-density planets transiting Kepler-11". Nature 470 (7332): 53–58. arXiv:1102.0291. Bibcode:2011Natur.470...53L. doi:10.1038/nature09760. Retrieved 4 February 2011.
- "Star : Kepler-11". Extrasolar Planets Encyclopaedia. Retrieved 4 February 2011.
- Borucki, W. J. et al. (2011), "Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data", The Astrophysical Journal 736: 19, arXiv:1102.0541, Bibcode:2011ApJ...736...19B, doi:10.1088/0004-637X/736/1/19
- Michael Mewhinney; Rachel Hoover; Trent J. Perrotto (2 February 2011). "NASA's Kepler Spacecraft Discovers Extraordinary New Planetary System". NASA. Retrieved 4 February 2011.
- Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
- Fraser Cain (September 15, 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
- Boyle, Alan (2 February 2011). "Planetary six-pack poses a puzzle". MSNBC Cosmic Log. Retrieved 4 February 2011.
- Naeye, Robert (2 February 2011). "Kepler's Outrageous System of Six Planets". Sky & Telescope. Retrieved 4 February 2011.
- John Matson (2 February 2011). "A Wealth of Worlds: Kepler Spacecraft Finds 6 New Exoplanets and Hints at 1,200 More". Scientific American. Retrieved 20 February 2011.
|Wikimedia Commons has media related to: Kepler-11|
- Official release: NASA's Kepler Spacecraft Discovers Extraordinary New Planetary System
- YouTube: Animation of Kepler-11 planetary system
- Kepler 11 Planetary System with Orbits and Planet Sizes