Harpalyke (moon)

Lore & Background

Harpalyke was discovered in November 2000, along with ten other Jovian moons by a team of astronomers from the University of Hawaiʻi led by Scott S. Sheppard and given the temporary designation S/2000 J 5. In October 2002, the moon was named after Harpalyce, the incestuous daughter of Clymenus, who in some accounts was also a lover of Zeus (Jupiter).

The satellite orbits Jupiter in the retrograde direction at a mean distance of 21,280,180 km and completes one orbit in 634.19 days. Its orbit has an inclination of 148° relative to the ecliptic and an eccentricity of 0.160, and is subject to continuous changes due to gravitational perturbation from the Sun and the other planets. Harpalyke belongs to the Ananke group, a group of irregular retrograde Jovian moons that orbit Jupiter at distances of approximately 19 to 22 million km, with orbital inclinations ranging from 144° to 156° and eccentricities between 0.10 and 0.30. The moons of the Ananke group are believed to be fragments of an asteroid or trans-Neptunian object that was gravitationally captured by Jupiter and destroyed by a collision several billion years ago.

Due to its small size, Harpalyke appears very faint from Earth with a visual apparent magnitude of around 22.2, so it can only be observed by very large, sensitive telescopes. Assuming Harpalyke has a low geometric albedo of 0.04 like other irregular moons, its diameter has been estimated to be 4 km. The shape of the moon is currently unknown, but given its small size, it is likely to have an irregular shape, similar to other small irregular moons. The satellite appears grey (color index R-V=0.43), similar to C-type asteroids.

Reader's Guide

Harpalyke is notable as a member of the Ananke group, a collection of irregular retrograde moons believed to be remnants of a captured asteroid or trans-Neptunian object that was shattered by a collision billions of years ago. Its discovery in November 2000 by Scott S. Sheppard and his team added to the growing catalog of Jupiter's irregular satellites, which provide insights into the dynamical history of the Jovian system. The moon's orbit, with a mean distance of about 21 million km and an inclination of 148°, is subject to gravitational perturbations from the Sun and other planets, illustrating the complex gravitational environment of the outer solar system. Although most of its physical properties are unknown, its estimated diameter of 4 km and grey color suggest it is a small, irregular, C-type asteroid-like body. Harpalyke has not been imaged up close by a space probe, but it is planned to be a distant observation target for the European Space Agency's Jupiter Icy Moons Explorer (Juice) mission, which will measure the rotation periods and shapes of Jupiter's irregular moons by watching their brightness change over time.

Did You Know?

• Harpalyke was discovered on 23 November 2000 by Scott S. Sheppard.
• It orbits Jupiter in the retrograde direction at an average distance of 21.0 million km.
• Harpalyke is a member of the Ananke group, believed to be fragments of a captured asteroid or trans-Neptunian object.
• The moon's estimated diameter is 4 km, and its surface is probably dark and gray in color.