Pasiphaë group

The Pasiphaë group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Pasiphaë and are thought to have a common origin.

Their semi-major axes (distances from Jupiter) range between 22.8 and 24.1 million km (the same range as the Carme group), their inclinations between 144.5° and 158.3°, and their eccentricities between 0.25 and 0.43.

Core members of the group include (from the largest to the smallest):^[1]

• Pasiphae
• Sinope, two-thirds the size of Pasiphaë
• Callirrhoe
• Megaclite
• Autonoe
• Eurydome
• Sponde

The International Astronomical Union (IAU) reserves names ending in -e for all retrograde moons, including this group's members.

Origin

The Pasiphaë group is believed to have been formed when Jupiter captured an asteroid which subsequently broke up after a collision. The original asteroid was not disturbed heavily: the original body is calculated to have been 60 km in diameter, about the same size as Pasiphaë; Pasiphaë retains 99% of the original body's mass. However, if Sinope belongs to the group, the ratio is much smaller, 87%.^[2]

Unlike the Carme and Ananke groups, the theory of a single impact origin for the Pasiphaë group is not accepted by all studies. This is because the Pasiphaë group, while similar in semi-major axis is more widely dispersed in inclination ¹ . However, Secular resonances, known for both Pasiphae and Sinope, could shape the orbits and provide the explanation for the post-collision dispersal of the orbital elements.^[3] Alternatively, Sinope might be not a part of the remnants of the same collision and captured independently instead.^[4]

The differences of colour between the objects (grey for Pasiphaë, light red for Callirrhoe and Megaclite) also suggest that the group could have a more complex origin than a single collision.^[4]

¹ Nesvorny 2003, concurring on Ananke and Carme groups, lists only Megaclithe for Pasiphae

References

1. ^ Scott S. Sheppard, David C. Jewitt, Carolyn Porco Jupiter's outer satellites and Trojans, In: Jupiter. The planet, satellites and magnetosphere. Edited by Fran Bagenal, Timothy E. Dowling, William B. McKinnon. Cambridge planetary science, Vol. 1, Cambridge, UK: Cambridge University Press, ISBN 0-521-81808-7, 2004, p. 263 - 280 Full text(pdf).
2. ^ Sheppard, Scott S.; Jewitt, David C. (May 5, 2003). "An abundant population of small irregular satellites around Jupiter". Nature 423 (6937): 261–263. doi:10.1038/nature01584. PMID 12748634.  However, Nesvorny 2003, while concurring on the Ananke and Carme groups, lists only Megaclithe for Pasiphaë's group
3. ^ David Nesvorný, Cristian Beaugé, and Luke Dones Collisional Origin of Families of Irregular Satellites, The Astronomical Journal, 127 (2004), pp. 1768–1783 Full text.
4. ^ ^{a b} Grav, Tommy; Holman, Matthew J.; Gladman, Brett J.; Aksnes, Kaare Photometric survey of the irregular satellites, Icarus, 166,(2003), pp. 33-45. Preprint