Helike

Helike was discovered on Feb. 6, 2003 by Scott S. Sheppard at the Mauna Kea Observatory in Hawaii.

Helike is a member of the Ananke group, a family of Jovian satellites which have similar orbits and are therefore thought to have a common origin. The group probably began as an asteroid that was captured by Jupiter's gravity and then suffered a collision, which broke off a number of pieces. The largest remaining chunk was named "Ananke," and the smaller pieces became the other 15 moons in the Ananke group.

All of the Ananke moons are retrograde, which means that they orbit Jupiter in the opposite direction from the planet's rotation. Their orbits are also eccentric (elliptical rather than circular) and rather highly inclined with respect to Jupiter's equatorial plane. All of these characteristics support the idea that the Ananke satellites began as a captured asteroid, rather than forming as part of the original Jupiter system. None of the Ananke members is massive enough to pull itself into a sphere, so they are probably all irregularly shaped.

Helike has a mean radius of about 1.2 miles (2 kilometers), assuming an albedo of 0.04. At a mean distance of about 13.1 million miles (21.1 million kilometers) from Jupiter, it takes about 626 Earth days to complete one orbit.

Originally called S/2003 J6, Helike was named for one of the Muses, who were daughters of Zeus, the Greek equivalent of the Roman god Jupiter. Helike is also the name of a nymph in Greek mythology who helped to nurse Zeus and was transferred to the stars as a reward. There, she became the constellation, the Great Bear.

A name ending in "e" was chosen in accordance with the International Astronomical Union's policy for designating outer moons with retrograde orbits.