Adrastea (moon)

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Image of Adrastea taken by Galileo's solid state imaging system between November 1996 and June 1997.
Discovered by David C. Jewitt
G. Edward Danielson
Discovery time July 8, 1979
Avgdistance from the center of its orbital path 129,000 km[1][2]
How egg-shaped its orbit is
How long it takes to complete an orbit 0.29826 d (7 h 9.5 min)[1][2]
Average speed 31.378 km/s[3]
Angle above the reference plane
0.03° (to Jupiter's equator)[1][2]
What it orbits Jupiter
Size and Other Qualities
Measures 20×16×14 km[4]
Average distance from its center to its surface 8.2 ± 2.0 km[4]
Volume inside it ~2,345 km³[3]
Mass ~2×1015 kg[3]
Average density 0.86 g/cm³ (assumed)
Gravity at its surface ~0.002 m/s² (0.0004 g)[3]
Slowest speed able to escape into space
("escape velocity")
~0.008 km/s[3]
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 ~0.1 ± 0.045[4]
Avg. surface temp. ~122 K

Adrastea or Jupiter XV, is the second closest moon to Jupiter. It was found by David C. Jewitt and G. Edward Danielson in Voyager 2 probe photographs taken in 1979 and received the designation S/1979 J 1.[5][6] In 1983, it was named after the mythological Adrastea,[7] who was a daughter of Jupiter and Ananke.

Adrastea was the first moon to be found from images taken by an interplanetary spacecraft, rather than through telescopic photography.

Physical characteristics[change | change source]

Adrastea is non-spherical and measures 20x16x14 km³ across.[4] What Adrastea is made of and the mass of Adrastea are not known, but assuming that its mean density is like that of Amalthea (~0.86 g/cm³)[8] its mass can be estimated at ~2×1015 kg. Amalthea's density implies that moon is composed of water ice with a porosity of 10-15%, and Adrastea may be similar.[8]

No surface details of Adrastea are known, due to the low resolution of available images.[4]

Discovery image of Adrastea, taken on July 8, 1979 by Voyager 2. Adrastea is the dot in the very middle, straddling the line of the Jovian rings.

Orbit[change | change source]

Adrastea is the smallest and second closest member of the closer moons to Jupiter. It orbits Jupiter at ~129,000 km (1.806 Jupiter radii) within the planet's Main Ring. The orbital eccentricity of ~0.0015 and inclination of ~ 0.03° relative to the equator of Jupiter are very small.[2]

Exploration[change | change source]

Adrastea was found in Voyager 1 and 2 images, but appeared only as a dot.[6] The Galileo spacecraft was able to see its shape, but the images remain poor.[4]

References[change | change source]

  1. 1.0 1.1 1.2 1.3 Evans, M.W.; Porco, C.C.; Hamilton, D.P. (2002). "The Orbits of Metis and Adrastea: The Origin and Significance of their Inclinations". Bulletin of the American Astronomical Society 34: 883.
  2. 2.0 2.1 2.2 2.3 2.4 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
  3. 3.0 3.1 3.2 3.3 3.4 Calculated on the basis of other parameters
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 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.
  5. IAUC 3454: Editorial Notice 1980 February 25 (discovery)
  6. 6.0 6.1 Jewitt, D.C.; Danielson, G.E.; Synnott, S.P. (1979). "Discovery of a New Jupiter Satellite". Science 206: 951.
  7. IAUC 3872: Satellites of Jupiter and Saturn 1983 September 30 (naming the moon)
  8. 8.0 8.1 Anderson, J.D.; Johnson, T.V.; Shubert, G.; et al. (2005). "Amalthea’s Density Is Less Than That of Water". Science 308: 1291–1293. doi:10.1126/science.1110422.

Other websites[change | change source]