Ananke

= Discovery =

Ananke was discovered by Seth Barnes Nicholson on September 28th 1951 by a photograph made by the 100-inch Hooker telescope at the Mount Wilson Observatory in California.

In-Depth
Ananke is the largest member of the Ananke group, with a mean radius of 14 kilometres (assuming an albedo of 0.04). The Ananke group is a family of Jovian satellites which have similar orbits and, therefore, must have common origins. Ananke was probably an asteroid that was captured by Jupiter's powerful gravity and the suffered a collision which broke off a number of pieces. Those pieces became the other 15 moons of the Ananke group.

All of the Ananke moons are retrograde, they orbit Jupiter in the opposite direction of the parent planet's rotation. Their orbits are also eccentric (elliptical rather than spherical). All of these characteristics support the idea that the Ananke satellites began as captured asteroids, rather than forming as part of Jupiter's original system. None of the Ananke moons are massive enough to pull themselves into a spherical shape, so they are probably irregularly shaped.

Ananke's observed colour appears to be somewhere between gray and light red. The Jovian satellite takes 630 Earth days to complete one orbit, with an average distance of 21.3 million kilometres away from Jupiter.

Namesake
Jovian satellites are usually named after Zeus/Jupiter lovers and descendants. Names of outer satellites with a prograde orbit usually end with the letter "a" (although an "o" has been reserved for unusual cases). Names of satellites with a retrograde orbit usually end with the letter "e".

Ananke was named after the mother of Adrastea by Zeus, the Greek equivalent of the Roman god Jupiter. In other words, Adrastea is described as a nymph of Crete who was once a nursemaid of Zeus.