 Artist's conception of a simultaneous transit of three planets before Kepler-11 observed by NASA's Kepler space telescope on Aug. 26, 2010. | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus[1] |
| Right ascension | 19h 48m 27.6226s[2] |
| Declination | +41° 54′ 32.903″[2] |
| Apparent magnitude (V) | 14.2[3] |
| Characteristics | |
| Spectral type | G6V[3] |
| Astrometry | |
| Proper motion (μ) | RA: 0.106(13)mas/yr[2] Dec.: −7.103(15)mas/yr[2] |
| Parallax (π) | 1.5476±0.0117 mas[2] |
| Distance | 2,110 ± 20 ly (646 ± 5 pc) |
| Absolute magnitude (MV) | 4.7[4] |
| Details[4] | |
| Mass | 1.042±0.005 M☉ |
| Radius | 1.021±0.025 R☉ |
| Surface gravity (log g) | 4.44±0.02 cgs |
| Temperature | 5836±7 K |
| Metallicity[Fe/H] | 0.062±0.007 dex |
| Rotational velocity (v sin i) | 2.2±0.2 km/s |
| Age | 3.2±0.9 Gyr |
| Other designations | |
| KOI-157,KIC 6541920,2MASS J19482762+4154328[5] | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
| KIC | data |
Kepler-11, also designated as2MASS J19482762+4154328,[6] is aSun-like star slightly larger than theSun in theconstellationCygnus, located some 2,110 light years fromEarth. It is located within the field of vision of theKepler space telescope, the satellite thatNASA'sKepler 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 yetdiscovered. 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 aboutNeptune's size.
Kepler-11 and its planets were discovered byNASA'sKepler Mission, a mission tasked with discovering planets intransit 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 ofEarth. Kepler-11 is the first discovered exoplanetary system with more than three transiting planets.[7]
Kepler-11 is named for the Kepler Mission: it is the 11th star with confirmed planets discovered in the Kepler field of view.The planets are named alphabetically, starting with the innermost:b,c,d,e,f, andg, distinguishers that are tagged onto the name of their home star.
Kepler-11 is aG-type star that is approximately 104% the mass of and 102% the radius of theSun. It has a surface temperature of about 5836K and is estimated to have an age of around 3.2 billion years.[4] In comparison, the Sun is about 4.6 billion years old[8] and has a surface temperature of 5778 K.[9]
With anapparent magnitude of 14.2, it is too faint to be seen with the naked eye.[3]
All known planetstransit the star; this means that all six planets' orbits appear to cross in front of their star as viewed from the Earth's perspective. Theirinclinations 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 morecoplanar (flatter) than theSolar System, where the corresponding figure is 2.3°.[3]
The estimated masses of planetsb -f fall in the range between those ofEarth andNeptune. Their estimated densities, all lower than that of Earth, imply that none of them have an Earth-like composition;[10] a significanthydrogen/helium atmosphere is predicted for planetsc,d,e,f, andg, while planetb may be surrounded by asteam atmosphere or perhaps by ahydrogen atmosphere.[11][12] The low densities likely result from high-volume extended atmospheres that surround cores of iron, rock, and possibly H2O.[12][13] The inner constituents of the Kepler-11 system were, at the time of their discoveries, the most comprehensively understood extrasolar planets smaller than Neptune.[14] Currently, observations do not place a firm constraint on the mass of planetg (<25ME).[11] However, formation and evolution studies indicate that the mass of planetg is not much greater than about 7ME.[12]
Kepler-11 planets may have formedin situ (i.e., at their observed orbital locations) orex situ, that is, they may have started their formation farther away from the star whilemigrating inward through gravitational interactions with a gaseousprotoplanetary disk. This second scenario predicts that a substantial fraction of the planets' mass is in H2O.[12] Regardless of the formation scenario, the gaseous component of the planets accounts for less than about 20% of their masses but for ≈40 to ≈60% of their radii. In 2014, the dynamical simulation shown what the Kepler-11 planetary system have likely to undergone a substantial inward migration in the past, producing an observed pattern of lower-mass planets on tightest orbits.[15] Additional yet unobserved gas giant planets on wider orbit are likely necessary for migration of smaller planets to proceed that far inward.[16]
The system is among the most compact known; the orbits of planetsb -f would easily fit inside the orbit ofMercury, withg only slightly outside it. Despite this close packing of the orbits, dynamical integrations indicate the Kepler-11 system has the potential to be stable on a time scale of billions of years.[3] However, it may be approaching instability due to asecular resonance involvingb andc. If this happens,b will most likely become eccentric enough that it collides withc.[17]
None of the planets are in low-ratioorbital resonances, in which multiple planets gravitationally tug on and stabilize each other's orbits, resulting in simple ratios of their orbital periods.[13] However,b andc areclose to a 5:4 ratio.[3]
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 howNeptune was discovered). The presence of additional gas giant planets is currently excluded up to orbital radius of 30AU.[18]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 2.78+0.64 −0.66 M🜨 | 0.091±0.001 | 10.3039+0.0006 −0.0010 | 0.045+0.068 −0.042 | 89.64+0.36 −0.18° | 1.83+0.07 −0.04 R🜨 |
| c | 5.0+1.3 −1.35 M🜨 | 0.107±0.001 | 13.0241+0.0013 −0.0008 | 0.026+0.063 −0.013 | 89.59+0.41 −0.16° | 2.87+0.05 −0.06 R🜨 |
| d | 8.13+0.67 −0.66 M🜨 | 0.155±0.001 | 22.6845±0.0009 | 0.004+0.007 −0.002 | 89.67+0.13 −0.16° | 3.12+0.06 −0.07 R🜨 |
| e | 9.48+0.86 −0.88 M🜨 | 0.195±0.002 | 31.9996+0.0008 −0.0012 | 0.012+0.006 −0.006 | 89.89+0.02 −0.02° | 4.19+0.07 −0.09 R🜨 |
| f | 2.43+0.49 −0.45 M🜨 | 0.250±0.002 | 46.6888+0.0027 −0.0032 | 0.013+0.011 −0.009 | 89.47±0.04° | 2.49+0.04 −0.07 R🜨 |
| g | <25 M🜨 | 0.466±0.004 | 118.3807+0.0010 −0.0006 | 0.013+0.011 −0.009 | 89.87+0.05 −0.06° | 3.33+0.06 −0.08 R🜨 |
 Relative size and positions of the 6 planets of Kepler-11, and of the innermostSolar System for comparison. The diameters of the planets (but not of the stars) are scaled up by a factor of 50. |
Kepler-11 system | ||
|---|---|---|
| Stars | | |
| Planets | ||
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