Praxidike was discovered on Nov. 23, 2000, by Scott S. Sheppard, David C. Jewitt, Yanga R. Fernandez, and Eugene Magnier at the Mauna Kea Observatory in Hawaii.


Praxidike 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. If Ananke, with a mean radius of 8.7 miles (14 kilometers), is considered the slightly diminished original asteroid, then Praxidike, with a mean radius of 2 miles (3.4 kilometers), assuming an albedo of 0.04, is the largest chip that was knocked off the asteroid.

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.

Praxidike is colored a similar gray to two other moons in the Ananke family: Harpalyke and Iocaste. At a mean distance of about 13 million miles (21.1 million kilometers) from Jupiter, Praxidike takes about 625 Earth days to complete one orbit.

How Praxidike Got Its Name

Originally called S/2000 J7, Praxidike was named for the Greek goddess of justice or punishment. She was the mother of Klesios, Harmonia and Arete by Zeus, the Greek equivalent of the Roman god Jupiter.

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

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