Pasiphaë group

The Pasiphaë group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Pasiphaë and are thought of 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):
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 [http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf Full text(pdf).] ]

* 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%. [cite journal
last = Sheppard
first = Scott S.
authorlink = Scott S. Sheppard
coauthors = Jewitt, David C.
title = An abundant population of small irregular satellites around Jupiter
journal = Nature
volume = 423
pages = 261–263
date = May 5, 2003
doi = 10.1038/nature01584 However, Nesvorny 2003, while concurring on the Ananke and Carme groups, lists only Megaclithe for Pasiphaë's group]

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.David Nesvorný, Cristian Beaugé, and Luke Dones"Collisional Origin of Families of Irregular Satellites", The Astronomical Journal, 127 (2004), pp. 1768–1783 [http://www.boulder.swri.edu/~davidn/papers/irrbig.pdf Full text.] ] Alternatively, Sinope might be not a part of the remnants of the same collision and captured independently instead. Grav, Tommy; Holman, Matthew J.; Gladman, Brett J.; Aksnes, Kaare "Photometric survey of the irregular satellites", Icarus, 166,(2003), pp. 33-45. [http://arxiv.org/abs/astro-ph/0301016 Preprint] ]

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.

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

References