Overview

Thelxinoe, also designated Jupiter XLII and originally S/2003 J 22, is one of Jupiter's many small irregular satellites. It was identified by a team associated with the University of Hawaii from images taken in 2003 and announced in 2004 by a team led by Scott S. Sheppard. Because of its small size and faintness it is observable only with large telescopes and sensitive detectors. The object is thought to measure roughly 2 kilometres across and has a dark, non-spherical form typical of irregular moons.

Physical characteristics

Thelxinoe is classified as a small, irregular satellite. Its approximate diameter of 2 km is inferred from its brightness assuming a low reflectivity (albedo) like that of many outer Solar System bodies. It is not spherical; instead its shape is likely elongated or irregular, a trait shared by many satellites of comparable size and noted in broader discussions of irregular moons (non-spherical). Surface composition is not well known because no close-up observations have been made.

Orbit and dynamical group

Thelxinoe follows a distant, retrograde orbit around Jupiter and is a member of the Ananke group, a cluster of moons that share similar orbital elements and are presumed to have a related origin (Ananke group). Key orbital parameters include:

  • Average orbital distance (semi-major axis): about 20,454,000 km
  • Orbital period: about 597.607 days
  • Inclination: about 151° to the ecliptic (approximately 153° relative to Jupiter's equator), indicating a retrograde motion
  • Eccentricity: roughly 0.2685, giving a noticeably elliptical orbit (eccentricity)

These values place Thelxinoe well within the radial range attributed to the Ananke group (approximately 19.3–22.7 million km) and with an inclination near 150°, consistent with a shared dynamical family.

Discovery and name

Images obtained in 2003 led to the object's initial identification and provisional designation S/2003 J 22; the discovery team published the observation in 2004. In March 2005 the moon received the name Thelxinoe, drawn from Greek mythology. Thelxinoe is traditionally cited by some classical sources as one of the original Muses (Muses) and as a daughter of Zeus (Zeus) and Mnemosyne (Mnemosyne), linking the modern name to the mythic lineage of Jupiter's namesake.

Origin, significance, and observation

Thelxinoe and other members of the Ananke group are generally regarded as captured objects or fragments from a parent body that was disrupted after capture by Jupiter's gravity. Their retrograde, inclined, and often eccentric orbits differ markedly from Jupiter's large regular moons, which formed in a circumplanetary disk. Studying such small irregular moons helps astronomers understand capture processes, collisional histories, and the population of minor bodies in the giant planet region. Observationally, Thelxinoe remains challenging to study: it is faint, small, and requires dedicated time on sizeable telescopes to refine its orbit or to attempt photometric or color measurements. Continued monitoring by teams and facilities that first found it and by later observers contributes to refining its orbit and to comparisons with related satellites.

Notable facts

  • Discovery announced in 2004 from 2003 images by a team led by Scott S. Sheppard.
  • Official name adopted in 2005 with mythological ties to the Muses and to Zeus.
  • Member of the retrograde Ananke group and shares the group's typical orbital range and inclination.
  • Orbital inclination is measured relative to the ecliptic, and its orbital eccentricity has been cataloged in planetary data sets (eccentricity).
  • Basic discovery and follow-up observations were conducted by researchers affiliated with institutions such as the University of Hawaii and teams that publish summaries of small outer satellites (Sheppard et al.).