Pasiphaë group — Jupiter’s retrograde irregular moons

Orbital characteristics and physical traits

Members of the group follow retrograde orbits (they orbit opposite to Jupiter’s rotation) with semi-major axes roughly between 22,800,000 and 24,100,000 km from the planet. Their orbital inclinations lie in the high-inclination range, typically between about 144.5° and 158.3°, and their orbital eccentricities are relatively large, commonly between about 0.25 and 0.43. These parameters contrast with Jupiter’s inner regular moons and place the Pasiphaë group among the distant irregular satellite population.

Origin and dynamical evolution

Most researchers interpret the Pasiphaë group as the remnants of a single body that was captured by Jupiter’s gravity and subsequently disrupted by collision or tidal stresses. After capture, collisional fragmentation can produce several fragments with related but not identical orbits, producing a broad cluster in orbital element space. Over time, gravitational perturbations, primarily from the Sun and Jupiter’s oblateness, and possible subsequent impacts have widened the spread of orbital elements seen today.

Notable members

The group contains a number of named satellites. Core and frequently cited members include:

• Pasiphaë (largest and name-bearing)
• Sinope (about two-thirds the size of Pasiphaë; sometimes regarded as marginal to the core group because of spectral and orbital differences)
• Callirrhoe
• Megaclite
• Autonoe
• Eurydome
• Sponde

These bodies are generally small and irregular in shape; measurements are challenging and in many cases only approximate sizes and surface properties are available from telescopic and spacecraft observations.

Context, naming and significance

The Pasiphaë group is often compared with other Jovian irregular families such as the Carme group, which occupies a similar radial zone but has different inclinations and other orbital characteristics. Studies of the group inform models of satellite capture, collisional fragmentation and the dynamical evolution of the outer Jovian system. The International Astronomical Union (IAU) follows a naming convention for Jupiter’s retrograde moons that assigns names ending in "-e"; this convention is reflected in many of the group members' names.

For further reading on irregular satellite classifications and dynamical families, see resources on orbital dynamics and satellite surveys (non-spherical physical types, orbital clustering studies, and analyses of eccentricity distributions). General discovery and designation notes for specific members are available in observational catalogs and mission reports (Sponde discovery notes and individual object pages such as Callirrhoe and Megaclite).

Ongoing observations continue to refine the orbits and physical properties of these faint objects; some bodies near the group boundaries may be interlopers or fragments from separate events, and spectroscopic surveys aim to clarify compositional links among the members.