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Thebe (moon)

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Image of Thebe taken by the Galileo spacecraft on January 4 2000.
Discovered by Stephen P. Synnott / Voyager 1
Discovery time March 5, 1979
Shortest distance from what it orbits around 218,000 km[1]
Longest distance from what it orbits around 226,000 km[1]
Avgdistance from the center of its orbital path 221889.0 ± 0.6 km (3.11 RJ)[2]
How egg-shaped its orbit is
0.0175 ± 0.0004[2]
How long it takes to complete an orbit 0.674536 ± 0.000001 d (16 h 11.3 min)[2]
Average speed 23.923 km/s[1]
Angle above the reference plane
1.076 ±0.003° (to Jupiter's equator)[2]
What it orbits Jupiter
Size and Other Qualities
Measures 116×98×84 km[3]
Average distance from its center to its surface 49.3 ± 2.0 km[3]
Volume inside it ~500,000 km³[1]
Mass 4.3×1017 kg[1]
Average density 0.86 g/cm³ (assumed)
Gravity at its surface ~0.020 m/s² (0.004 g)[1]
Slowest speed able to escape into space
("escape velocity")
~0.040 km/s[1]
How long it takes to turn around one time synchronous
Angle at which it turns
(in relation to its orbit)
How much light it reflects 0.047 ± 0.003[4]
Avg. surface temp. ~124 K

Thebe or Jupiter XIV, is the fourth of Jupiter's known moons (by distance from the planet). It was found by Stephen P. Synnott in images from the Voyager 1 space probe taken on March 5, 1979 and was given the 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 the daughter of the river god Asopus and a lover of Zeus (the Greek equivalent of Jupiter).[7]


Thebe is the farthest 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 orbital eccentricity of ~0.018 and an inclination of ~1.08° relative to the equator of Jupiter.[2] These values are unusually high for a closer moon and can be explained by the past influence of the closest Galilean satellite Io; in the past, several mean motion resonances with Io would have passed through Thebe's orbit as Io gradually moved away from Jupiter, and these excited Thebe's orbit.[8]

Physical characteristics

Thebe is not a sphere, 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.

The surface of Thebe is dark and appears to be reddish in color.[4]


Thebe was found in Voyager 1 images by Steve Synnott, a member of the Voyager navigation team.[6] However, before the Galileo spacecraft arrived at Jupiter, little was known about it. Galileo imaged almost all of the surface of Thebe and put constraints on its composition.[3]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Calculated on the basis of other parameters
  2. 2.0 2.1 2.2 2.3 2.4 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:10.1016/j.icarus.2005.11.007 .
  3. 3.0 3.1 3.2 3.3 Thomas, P.C.; Burns, J.A.; Rossier, L.; et al. (1998). "The Small Inner Satellites of Jupiter". ICARUS 135: 360–371. doi:10.1006/icar.1998.5976 .
  4. 4.0 4.1 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:10.1006/icar.2000.6474 .
  5. IAUC 3470: Satellites of Jupiter 1980 April 28 (discovery)
  6. 6.0 6.1 Synnott, S.P. (1980). "1979J2: The Discovery of a Previously Unknown Jovian Satellite". Science 210 (4471): 786-788.
  7. IAUC 3872: Satellites of Jupiter and Saturn 1983 September 30 (naming the moon)
  8. 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

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