Ananke group

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

Their semi-major axes (distances from Jupiter) range between 19.3 and 22.7 Gm, their orbital inclinations between 145.7° and 154.8°, and their orbital eccentricities between 0.02 and 0.28.

The core members include (from largest to 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).] ] 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.] ]
*Ananke
*Praxidike
*Iocaste
*Harpalyke
*Thyone
*Euanthe
*Euporie

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

Origin

The Ananke group is believed to have been formed when an asteroid was captured by Jupiter and subsequently fragmented by a collision. This belief is founded on the fact that the dispersion of the mean¹ orbital parameters of the core members is very small and can be accounted for by a small velocity impulse (15 < δV < 80 m/s), compatible with a single collision and breakup. David Nesvorný, Jose L. A. Alvarellos, Luke Dones, and Harold F. Levison"Orbital and Collisional Evolution of the Irregular Satellites", The Astronomical Journal,126 (2003), pages 398–429. [http://www.journals.uchicago.edu/AJ/journal/issues/v126n1/202528/202528.web.pdf (pdf)] ]

Based on the sizes of the satellites, the original asteroid may have been about 28 km in diameter. Since this value is near the approximate diameter of Ananke itself, it is likely the parent body was not heavily disrupted. [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 [http://www.ifa.hawaii.edu/~jewitt/papers/JSATS/SJ2003.pdf (pdf).] ]

Available photometric studies add further credibility to the common origin thesis: three of the moons of the family (Harpalyke, Praxidike and Iocaste) display similar grey colours (average colour indices: B−V = 0.77 and V−R = 0.42) while Ananke itself is on the boundary between grey and light red.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] ]

¹Osculating orbital parameters of irregular satellites of Jupiter change widely in short intervals due to heavy perturbation by Jupiter. For example, changes of as much as 1 Gm in semi-major axis in 2 years, 0.5 in eccentricity in 12 years, and as much as 5° in 24 years have been reported. Mean orbital elements are the averages calculated by the numerical integration of current elements over a long period of time, used to determine the dynamical families.

References