Mneme (Jupiter XL) — an irregular, retrograde moon of Jupiter

Physical characteristics

Mneme is estimated to be about 2 kilometres in diameter, which makes it far too small for gravity to shape it into a sphere; hence it is described as non-spherical. Its surface properties are not well measured because the object is dim and distant. By analogy with other small, irregular Jovian satellites, Mneme is presumed to be dark and composed of primitive, carbon-rich material, but specific spectral observations are limited.

Orbit and group membership

Mneme orbits Jupiter at an average distance of roughly 21,427,000 kilometres and completes one circuit in about 640.769 days. Its orbit is noticeably inclined and eccentric: the inclination is about 149° to the ecliptic (around 148° relative to Jupiter's equator), and the orbital eccentricity is approximately 0.2214. These parameters place Mneme among the retrograde irregular satellites that occupy distant, inclined, and often elliptical paths around Jupiter.

• Average orbital radius: ~21,427,000 km
• Orbital period: ~640.769 days
• Inclination: ~149° to the ecliptic
• Eccentricity: ~0.2214

Mneme is considered part of the Ananke group, a cluster of retrograde moons that share similar orbital distances (roughly 19.3–22.7 million km) and inclinations near 150°. Members of this group are believed to have a related origin, often interpreted as fragments of a single captured body that was later broken apart.

Discovery, name and mythology

The discovery team reported Mneme in 2003; further observations allowed its orbit to be determined and the moon to be officially named in March 2005. The name comes from Mneme, one of the original Muses in Greek tradition. Mneme is sometimes conflated with Mnemosyne, who is described in myth as the mother of the Muses by Zeus. The naming follows the convention of assigning names from classical mythology to Jovian satellites and helps distinguish this moon from other small bodies.

Origins, significance and observation

Mneme and other small irregular satellites are of interest because they preserve clues about early solar-system processes and the capture of minor bodies by giant planets. The Ananke group in particular supports the hypothesis of a captured progenitor that fragmented under tidal forces or a collisional event. Observationally, Mneme remains a challenging target: its faintness restricts detailed study to large ground-based telescopes and dedicated surveys. Amateur and professional observers refer to published ephemerides and discovery papers (see linked sources) when planning observations.

For further contextual reading and data on irregular Jovian satellites, consult discovery reports and group studies; primary references include the discovery announcement and surveys led by the University of Hawaii team and subsequent orbital analyses by planetary astronomers. Related terms and resources: non-spherical, the discovery team at University of Hawaii, lead discoverer Scott S. Sheppard, discovery year 2003, orbital plane reference ecliptic, orbital parameter eccentricity, the Muses, mythological figure Mnemosyne, mythological consort Zeus, and the Ananke group.