Thebe (moon)
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Discovery
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| Discovered by | Stephen P. Synnott / Voyager 1 |
| Discovery date | March 5, 1979 |
| Periapsis | 218,000 km[1] |
| Apoapsis | 226,000 km[1] |
| Mean orbit radius | 221889.0 ± 0.6 km (3.11 RJ)[2] |
| Eccentricity | 0.0175 ± 0.0004[2] |
| Orbital period | 0.674536 ± 0.000001 d (16 h 11.3 min)[2] |
| Average orbital speed | 23.923 km/s[1] |
| Inclination | 1.076 ±0.003° (to Jupiter's equator)[2] |
| Satellite of | Jupiter |
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Physical characteristics
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| Dimensions | 116×98×84 km[3] |
| Mean radius | 49.3 ± 2.0 km[3] |
| Volume | ~500,000 km³[1] |
| Mass | 4.3×1017 kg[1] |
| Mean density | 0.86 g/cm³ (assumed) |
| Equatorial surface gravity | ~0.020 m/s² (0.004 g)[1] |
| Escape velocity | ~0.040 km/s[1] |
| Rotation period | synchronous |
| Axial tilt | zero |
| Albedo | 0.047 ± 0.003[4] |
| Temperature | ~124 K |
Thebe (thee'-bee, IPA: /ˈθiːbi/, Greek Θήβη) or Jupiter XIV, is the fourth of Jupiter's known moons (by distance from the planet). It was discovered by Stephen P. Synnott in images from the Voyager 1 space probe taken on March 5, 1979 and was initially given the provisional designation S/1979 J 2.[5][6] Later, it was found on images dating back to February 27, 1979. In 1983 it was officially named after the mythological nymph Thebe who was a lover of Zeus (the Greek equivalent of Jupiter).[7]
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[edit] Orbit
Thebe is the outermost of the inner Jovian moons. It orbits Jupiter at a distance of ~222,000 km (3.11 Jupiter radii). The orbit of Thebe has an eccentricity of ~0.018 and an inclination of ~1.08° relative to the equator of Jupiter.[2] These values are unusually high for an inner satellite and can be explained by the past influence of the innermost Galilean satellite Io; in the past, several mean motion resonances with Io would have passed through Thebe's orbit as Io gradually receded from Jupiter, and these excited Thebe's orbit.[8]
The orbit of Thebe lies near the outer edge of the Thebe Gossamer Ring, which is composed of the dust ejected from the satellite.[9]
[edit] Physical characteristics
Thebe is irregularly shaped, with the closest ellipsoidal approximation being 116x98x84 km. Its bulk density and mass are not known but assuming that it mean density is like that of Amalthea (~0.86 g/cm³)[3] its mass can be estimated at ~4.3×1017 kg.
Thebe rotates synchronously with its orbital period, keeping one face always looking toward the planet, similarly to all inner satellites of Jupiter. Its orientation is such that the long axis always points to Jupiter. At the surface points closest to and furthest from Jupiter, the surface is thought to near the edge of the Roche lobe where Thebe's gravity is almost balanced by the centrifugal force. As a result, the escape velocity there is very small, allowing dust to escape easily after meteorite impacts to form the Thebe Gossamer Ring.[8]
The surface of Thebe is dark and appears to be reddish in color.[4] There is a substantial asymmetry between leading and trailing hemispheres: the leading hemisphere is 1.3 times brighter than the trailing one. The asymmetry is probably caused by the higher velocity and frequency of impacts on the leading hemisphere, which excavate a bright material (ice) from the interior of the moon.[4] The surface of Thebe is heavily cratered. There appear to be at least three or four impact craters that are very large: each is roughly comparable in size to Thebe's own diameter. The largest (~40 km) crater is situated on the anti-Jovian side of the moon and is called Zethus (the only surface feature on Thebe to have received a name). There are several bright spots at the rim of this crater.[3]
[edit] Exploration
Thebe was discovered in Voyager 1 images by Steve Synnott, a member of the Voyager navigation team.[6] However, before the Galileo spacecraft arrived at Jupiter, knowledge about it was very limited. Galileo imaged almost all of the surface of Thebe and put constraints on its composition.[3]
[edit] See also
[edit] References
- ^ a b c d e f g Calculated on the basis of other parameters
- ^ a b c d e Cooper, N.J.; Murray, C.D.; Porco, C.C.; Spitale, J.N. (2006). "Cassini ISS astrometric observations of the inner jovian satellites, Amalthea and Thebe". ICARUS 181: 223–234. doi:.
- ^ a b c d e Thomas, P.C.; Burns, J.A.; Rossier, L.; et.al. (1998). "The Small Inner Satellites of Jupiter". ICARUS 135: 360–371. doi:.
- ^ a b c Simonelli, D.P.; Rossiery, L.; Thomas, P.C.; et.al. (2000). "Leading/Trailing Albedo Asymmetries of Thebe, Amalthea, and Metis". ICARUS 147: 353–365. doi:.
- ^ IAUC 3470: Satellites of Jupiter 1980 April 28 (discovery)
- ^ a b Synnott, S.P. (1980). "1979J2: The Discovery of a Previously Unknown Jovian Satellite". Science 210 (4471): 786-788.
- ^ IAUC 3872: Satellites of Jupiter and Saturn 1983 September 30 (naming the moon)
- ^ a b Burns, J.A.; D.P. Simonelli & M.R. Showalter et al. (2004), "Jupiter’s Ring-Moon System", in Bagenal, F.; Dowling, T. E.; McKinnon, W. B., Jupiter: The planet, Satellites and Magnetosphere, Cambridge University Press, <http://www.astro.umd.edu/~hamilton/research/preprints/BurSimSho03.pdf>
- ^ Burns, J.A.; Showalter, M.R.; Hamilton, D.P.; et.al. (1999). "The Formation of Jupiter's Faint Rings". Science 284: 1146-1150. doi:.
[edit] External links
Thebe Profile by NASA's Solar System Exploration
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