Ananke (moon)
Ananke also known as , 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 by Zeus. Ananke did not receive its present name until 1975; before then, it was simply known as . It was sometimes called "Adrastea" between 1955 and 1975.
Orbit
Image:TheIrregulars [JUPITER retro.svg|thumb|left|300px|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 a high-eccentricity and high-inclination 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
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. 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.