Ananke (/əˈnæŋki/) also known as Jupiter XII, is a one of larger retrograde irregular moon of Jupiter.

Discovery and Naming

It was discovered by Seth Barnes Nicholson at Mount Wilson Observatory in 1951.

It is named after the Greek mythological Ananke, the personification of necessity, and the mother of the Moirai (Fates) by Zeus. Ananke did not receive its present name until 1975; before then, it was simply known as Jupiter XII. It was sometimes called "Adrastea" between 1955 and 1975 (Adrastea is now the name of another satellite of Jupiter).

Orbit

The diagram illustrates Ananke's orbit in relation to other retrograde irregular satellites of Jupiter. The eccentricity of selected orbits is represented by the yellow segments (extending from the pericentre to the apocentre). The outermost regular satellite Callisto is located for reference.

Ananke orbits Jupiter (on average 21,042,470 km) on a high-eccentricity (0,174) and high-inclination (149° to ecliptic) retrograde orbit. They are continuously changing due to solar and planetary perturbations.

Ananke gives its name to the Ananke group, of irregular retrograde moons orbiting Jupiter at a distance ranging between 19–22 million km, inclinations between 144 and 156°, and eccentricities between 0.10 and 0.30.

Physical characteristics

Single-exposure image of Ananke by the Wide-field Infrared Survey Explorer (WISE) spacecraft in 2010

From infrared thermal measurements by the WISE spacecraft, Ananke's albedo is measured at 3,8 %, corresponding to a diameter of 29,1 kilometres.

In the visible spectrum, Ananke appears neutral to light-red (colour indices B-V=0.90 V-R=0.38). The infrared spectrum is similar to P-type asteroids but with a possible indication of water.

The rotation period is approximately 8 hours and 18.6 minutes with a peak amplitude of about ~0.4 magnitudes.

Origin

Ananke probably did not form near Jupiter but was captured by Jupiter later. Given these orbital elements and the physical characteristics known so far, Ananke is thought to be the largest remnant of an original break-up, forming the Ananke group.

See also

External links

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