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# Ananke (moon)

Ananke
Discovery
Discovered by S. B. Nicholson
Discovery time September 28, 1951
Orbit
Shortest distance from what it orbits around 12,567,000 km
Longest distance from what it orbits around 29,063,500 km
Avgdistance from the center of its orbital path 21,280,000 km[1]
How egg-shaped its orbit is
("eccentricity")
0.24[1]
How long it takes to complete an orbit 610.45 d (1.680 a)[1]
Average speed 2.367 km/s
Angle above the reference plane
("inclination")
148.89° (to the ecliptic)
149.9° (to Jupiter's equator)[1]
What it orbits Jupiter
Size and Other Qualities
Average distance from its center to its surface 14 km[2]
Area of its surface ~2500 km²
Volume inside it ~11,500 km³
Mass 3.0×1016 kg
Average density 2.6 g/cm³ (assumed)
Gravity at its surface 0.010 m/s2 (0.001 g)
Slowest speed able to escape into space
("escape velocity")
~0.017 km/s
How much light it reflects 0.04 (assumed)[2]
Avg. surface temp. ~124 K

Ananke is a retrograde non-spherical moon of Jupiter. It was found by Seth Barnes Nicholson at Mount Wilson Observatory in 1951[3] and is named after the mythological Ananke, the mother of Adrastea by Jupiter. The adjectival form of the name is Anankean.

Ananke did not get its present name[4] until 1975;[5] before then, it was simply known as Jupiter XII. It was sometimes called "Adrastea"[6] between 1955 and 1975. Note that Adrastea is now the name of another moon of Jupiter.

Ananke gives its name to the Ananke group, retrograde non-spherical moons which orbit Jupiter between 19,300,000 and 22,700,000 km, at inclinations of about 150°.[2]

## Orbit

Ananke orbits Jupiter on a high eccentricity and high inclination retrograde orbit. Eight non-spherical moons found since 2000 follow similar orbits.[2] The orbital elements are as of January 2000.[1] They are changing a lot due to Solar and planetary perturbations. The diagram illustrates Ananke's orbit in relation to other retrograde non-spherical moons of Jupiter. The eccentricity of selected orbits is represented by the yellow segments (extending from the pericentre to the apocentre). The farthest spherical moon Callisto is located for reference.

Given these orbital elements and the physical characteristics known so far, Ananke is thought to be the biggest remnant[7] of an original break-up forming the Ananke group.[8][9]

## Physical characteristics

In the visible spectrum, Ananke appears grey to light-red.[9]

The infrared spectrum is similar to P-type asteroids but with a possible indication of water.[10]

## References

1. Jacobson, R. A. (2000). "The Orbits of Outer Jovian Satellites". Astronomical Journal 120: pp. 2679-2686. .
2. Sheppard, S. S., Jewitt, D. C., Porco, C.; Jupiter's Outer Satellites and Trojans, in Jupiter: The Planet, Satellites and Magnetosphere, edited by Fran Bagenal, Timothy E. Dowling, William B. McKinnon, Cambridge Planetary Science, Vol. 1, Cambridge, UK: Cambridge University Press, ISBN 0-521-81808-7, 2004, pp. 263-280
3. Nicholson, S. B. (1951). "An unidentified object near Jupiter, probably a new satellite". Publications of the Astronomical Society of the Pacific 63 (375): 297–299.
4. Nicholson, S.B. (April 1939). "S. B. Nicholson declines to name the satellites of Jupiter he has discovered". Publications of the Astronomical Society of the Pacific 51 (300): 85–94.
5. Marsden, B. G. (7 October 1974). "Satellites of Jupiter". IAUC Circular 2846.
6. Payne-Gaposchkin, Cecilia; Katherine Haramundanis (1970). Introduction to Astronomy. Englewood Cliffs, N.J.: Prentice-Hall. .
7. Sheppard, S.S.; Jewitt, D.C. (2003). "An abundant population of small irregular satellites around Jupiter". Nature 423: 261-263.
8. Nesvorný, D.; Beaugé, C.;Dones, L. (2004). "Collisional Origin of Families of Irregular Satellites". The Astronomical Journal 127: 1768–1783.
9. Grav, Tommy (2003). "Photometric survey of the irregular satellites". Icarus 166: 33-45. .
10. Grav, Tommy (2004). "Near-Infrared Photometry of the Irregular Satellites of Jupiter and Saturn". The Astrophysical Journal 605: L141–L144.
1. Ephemeris IAU-MPC NSES