| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Lyra |
| Right ascension | 19h 10m 47.52334s[1] |
| Declination | +42° 20′ 19.3014″[1] |
| Apparent magnitude (V) | 12.51[2] |
| Characteristics | |
| Spectral type | G8V[3] |
| Astrometry | |
| Radial velocity (Rv) | −21.98±0.92[1] km/s |
| Proper motion (μ) | RA: −3.869mas/yr[1] Dec.: −27.105mas/yr[1] |
| Parallax (π) | 3.4936±0.0095 mas[1] |
| Distance | 934 ± 3 ly (286.2 ± 0.8 pc) |
| Details | |
| Mass | 0.929±0.053[4] M☉ |
| Radius | 0.9164+0.0087 −0.0077[4] R☉ |
| Temperature | 5495±50[4] K |
| Metallicity [Fe/H] | 0.07±0.08[4] dex |
| Age | 5.6+4.5 −3.5[4] Gyr |
| Other designations | |
| KOI-070, KIC 6850504,2MASS J19104752+4220194, Gaia DR2 2102548708017562112.[3] | |
| Database references | |
| SIMBAD | data |
| KIC | data |
Kepler-20 is a star about 934light-years (286parsecs) from Earth in the constellationLyra with a system of at least five, and possibly six, known planets.[5] The apparent magnitude of this star is 12.51, so it cannot be seen with the unaided eye. Viewing it requires a telescope with anaperture of 15 cm (6 in) or more.[6] It is slightly smaller than the Sun, with 94% of theSun's radius and about 91% of theSun's mass. Theeffective temperature of thephotosphere is slightly cooler than that of the Sun at5466 K, giving it the characteristic yellow hue of astellar class G8 star.[7][8] The abundance of elements other than hydrogen or helium, what astronomers term themetallicity, is approximately the same as in the Sun. It may be older than the Sun, although the margin of error here is relatively large.[9]
On December 20, 2011, theKepler Space Telescope team reported the discovery of a five-planet system containing three small gas giants and the first twoEarth-sizedextrasolar planets,Kepler-20e (the first known extrasolar planet smaller thanEarth orbiting a main-sequence star)[10] andKepler-20f, orbiting aSun-like star.[11] Although the planets areEarth-sized, they are notEarth-like in the respect that they are much closer to their star than Earth, and are hence not near the habitable zone,[12] with expected surface temperatures of 760 °C (1,400 °F) and 427 °C (801 °F), respectively. The three otherNeptune-sized planets in the system,Kepler-20b,Kepler-20c, andKepler-20d, all orbit similarly close to the star.[13][14]
Only upper limits on the masses of e and f are known. Their masses are uncertain as they are too small to detect viaradial velocity with current technology.[8] As of 2023[update], Kepler-20e is known to be less massive than Earth.[4]
A 2016 study detected a sixth planet in the system based on radial velocity observations. Kepler-20g may be a non-transiting Neptunian world.[15] However, the existence of this planet was challenged in 2019,[16] and a non-detection was reported in 2023.[4] Another 2023 study listed this planet, though the data used was identical to the 2016 study except for the addition of a single data point, and the dispute was not addressed.[17]: 24
All planets are at smallnear resonances; proceeding outwards, they are 3:2, 4:2, 2:1, 4:1. The planetary orbits in current form are highly sensitive to perturbations caused by outer planets, therefore assuming stability, no additional gas giant planets can be located closer than 30AU from the parent star.[18]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 9.7±1.3 M🜨 | 0.04565±0.00089 | 3.6961049(16) | <0.083 | 87.36+0.22 −1.6° | 1.773+0.053 −0.030 R🜨 |
| e | <0.76 M🜨 | 0.0637±0.0012 | 6.0984882(99) | <0.092 | 87.63+1.1 −0.13° | 0.821±0.022 R🜨 |
| c | 11.1±2.1 M🜨 | 0.0936±0.0018 | 10.8540774(21) | <0.076 | 89.815+0.036 −0.63° | 2.894+0.036 −0.033 R🜨 |
| f | <1.4 M🜨 | 0.1387±0.0027 | 19.578328(48) | <0.094 | 88.788+0.43 −0.072° | 0.952+0.047 −0.087 R🜨 |
| g(disputed) | ≥19.96+3.08 −3.61M🜨 | 0.2055+0.0022 −0.0021 | 34.940+0.038 −0.035 | ≤0.16 | — | — |
| d | 13.4+3.7 −3.6 M🜨 | 0.3474±0.0067 | 77.611455(96) | <0.082 | 89.708+0.17 −0.053° | 2.606+0.053 −0.039 R🜨 |
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