Ananke (moon)

Physical characteristics

Ananke is dark and irregular in shape, lacking the spherical form seen in larger moons. Like many distant Jovian irregulars, it has a low surface reflectivity and a heavily cratered, uneven surface consistent with old, primitive material. Precise measurements of its size and composition are limited; published sources describe Ananke as a small body comparable to other irregular satellites, likely composed of rock and carbon-rich (primitive) material. Its adjectival form is Anankean.

Orbit and group

Ananke follows a retrograde orbit, meaning it moves around Jupiter in the opposite sense to the planet's rotation. It orbits at a large distance from Jupiter and has a high orbital inclination relative to the planet's equator. Because its orbit and those of several other moons are similar, Ananke lends its name to the Ananke group, a cluster of retrograde irregular moons orbiting Jupiter at comparable distances and inclinations. The group's defining range and typical inclination are summarized in specialist lists; see the grouped classification at Ananke group for more context.

Discovery and naming

Ananke was discovered by astronomer Seth B. Nicholson at Mount Wilson Observatory in 1951 and was given the provisional designation Jupiter XII. The discovery is commonly cited in historical lists of Jovian satellites; original discovery notes can be consulted via discovery references such as observatory records. Between 1955 and 1975 the moon was sometimes informally called "Adrastea," a name that later became associated with a different, inner Jovian satellite; for the currently accepted usage see the note on Adrastea. The International Astronomical Union assigned the name Ananke in 1975, drawing on the Greek mythological figure who is traditionally associated with necessity and is said to be the mother of Adrastea.

Scientific importance and notable facts

Ananke and the other irregular satellites are important for understanding the capture and collisional history of the Jovian system. Studies of their orbits, colors, and relative distributions help astronomers test models in which a larger captured body fragmented to produce the present clusters, or in which multiple capture events supplied the irregular population. Observations of Ananke contribute to constraints on such formation scenarios and on the dynamical evolution of Jupiter's distant satellite system.

For general background and curated lists of Jovian moons see general satellite catalogs and overviews; further curated summaries are available from resources such as naming and cataloging references and astronomical databases that compile orbital parameters and discovery details (see classification). Historical references and discovery notes are also collected in institutional archives (discovery source).