Thyone

Thyone was discovered on Dec. 11, 2001, by Scott S. Sheppard, David C. Jewitt and Jan T. Kleyna at the Mauna Kea Observatory in Hawaii.

Thyone 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.

Thyone has a mean radius of about 1 mile (2 kilometers), assuming an albedo of 0.04. At a mean distance of about 13.2 million miles (21.2 million kilometers) from Jupiter, it takes about 627 Earth days to complete one orbit.

Originally called S/2001 J2, Thyone was named for the mother (originally named Semele) of Dionysos by Zeus, the Greek equivalent of the Roman god Jupiter. Her story is similar to that of Lysithea, namesake of another Jovian moon: Zeus promised to do whatever she asked after he impregnated her, and Hera (Zeus' wife and sister) tricked her into asking Zeus to come to her in the same way he appeared before Hera. So Zeus presented himself accompanied by lightning and thunder, which literally scared Thyone to death. Zeus sewed her fetus into his own thigh, so he could carry the child to term. At the appropriate time, Zeus undid the stitches and out popped Dionysus.

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