Cyllene (Jupiter XLVIII) — small retrograde moon of Jupiter

Discovery and designation

Cyllene was discovered in 2003 by a team at the University of Hawaii led by Scott S. Sheppard; the discovery announcement lists the finding team and observing circumstances. The formal discoverer affiliation is often cited as the University of Hawaii team, and individual researchers such as Scott S. Sheppard are commonly credited. Following standard practice for tiny outer satellites, it received the provisional name S/2003 J 13 until a mythological name was assigned.

Orbit and physical characteristics

Cyllene orbits Jupiter at an average distance of about 23,396,000 kilometres and has an orbital period of approximately 731.1 days. Its path is notably eccentric (orbital eccentricity about 0.4116) and inclined roughly 140° to the ecliptic, which corresponds to a retrograde sense of motion relative to Jupiter's rotation. For a summary of orbital elements and related terminology see orbit, ecliptic and eccentricity. The object is small and non-spherical, so its brightness and shape indicate a few-kilometre irregular body rather than a round moon (non-spherical).

Name and mythological origin

In March 2005 the International Astronomical Union assigned the name Cyllene, drawn from Greek mythology. Cyllene was a nymph—sometimes described as a naiad (water nymph) or an oread (mountain nymph)—associated with Mount Kyllini, which is referenced geographically at Mount Kyllini in Greece. Mythical accounts link her to Zeus (Jupiter), which follows the IAU practice of naming Jovian moons after figures connected with Zeus/Jupiter.

Group membership and origin

Cyllene is identified as a member of the Pasiphaë group, an assemblage of irregular, retrograde Jovian satellites that orbit at similar distances and inclinations. The group — summarized at Pasiphaë group — typically ranges in orbital distance and shows similar retrograde inclinations, suggesting a common origin such as capture of an object followed by collisional fragmentation. The retrograde character of its motion is highlighted by the classification retrograde, and many members in this population are small, irregular fragments rather than intact large moons.

Observing Cyllene and significance

Because Cyllene is faint and small, it is observable only with large telescopes and sensitive detectors; tracking such faint outer moons helps refine models of Jupiter's satellite system and the Solar System's capture processes. Observations that characterize its light curve, orbit, and spectral properties can illuminate its relationship to other Pasiphaë-group objects and the history of collisions or capture. For basic reference and catalog entries see sources marked as moon of Jupiter and observational summaries from discovery teams such as University of Hawaii and researchers like Scott S. Sheppard.