Iocaste (moon)

Lore & Background

Iocaste was discovered on 23 November 2000 by a team from the University of Hawaiʻi led by Scott S. Sheppard, along with ten other Jovian moons, and given the temporary designation S/2000 J 3. It was named in October 2002 after Jocasta, the mother/wife of Oedipus in Greek mythology, with the name ending in 'e' following IAU policy for retrograde outer moons.

The satellite orbits Jupiter in the retrograde direction at an average distance of 21.0 million km, completing one orbit in 640.97 days. Its orbit has an inclination of 149° and an eccentricity of 0.329, and is subject to continuous changes due to gravitational perturbation from the Sun and other planets. Iocaste belongs to the Ananke group, sharing similar orbital properties with the larger irregular moon Ananke; members of this group orbit at distances of roughly 19 to 22 million km with inclinations of 144° to 156° and eccentricities between 0.10 and 0.30.

Most of Iocaste's physical properties are unknown. It is estimated to be about 5 km in diameter, assuming a low geometric albedo of 0.04 like other irregular moons. Its surface is probably dark and gray in color, with a color index similar to C-type asteroids. The moon has not been imaged up close by a space probe; the European Space Agency's Juice mission plans to observe it distantly to measure its rotation period and shape by watching brightness changes over time.

Reader's Guide

Iocaste's significance lies in its membership in the Ananke group, which provides evidence for a common origin as fragments of an asteroid or trans-Neptunian object captured by Jupiter and destroyed by a collision billions of years ago. As a small irregular moon with a retrograde orbit, it helps astronomers understand the dynamics and history of Jupiter's outer satellite system. Its discovery in 2000 by Scott S. Sheppard's team added to the growing catalog of Jovian irregular moons, and its naming after Jocasta follows IAU conventions for retrograde moons. Although most of its physical properties remain unknown, its estimated diameter of 5 km and gray surface color suggest it is similar to C-type asteroids. The planned distant observations by the Juice mission may reveal its rotation period and shape, contributing to knowledge of these faint, distant objects. Iocaste's orbit, subject to gravitational perturbations, also illustrates the complex gravitational environment of the Jovian system.

Did You Know?

• Iocaste was discovered on 23 November 2000 by Scott S. Sheppard and a team from the University of Hawaiʻi.
• The moon has not been imaged up close by any space probe; the Juice mission plans distant observations.