Editing Ananke group (section)

==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 relation|dispersion]] of the [[Proper orbital elements|mean orbital parameters]]{{Efn|[[Osculating orbit|Osculating orbital parameters]] of irregular satellites of Jupiter change widely in short intervals due to heavy [[Perturbation (astronomy)|perturbation]] by the Sun. 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 inclination 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.}} of the core members is very small and can be accounted for by a small velocity impulse (15 < δV < 80&nbsp;m/s), compatible with a single collision and breakup.<ref name="Nesvorny2003">{{Cite journal |last1=Nesvorný |first1=David |last2=Alvarellos |first2=Jose L. A. |last3=Dones |first3=Luke |last4=Levison |first4=Harold F. |date=July 2003 |title=Orbital and Collisional Evolution of the Irregular Satellites |url=http://www.boulder.swri.edu/~davidn/papers/irrbig.pdf |journal=[[The Astronomical Journal]] |volume=126 |issue=1 |pages=398–429|doi=10.1086/375461 |bibcode=2003AJ....126..398N |s2cid=8502734 }}</ref>

Based on the sizes of the satellites, the original asteroid may have been about 28&nbsp;km in diameter. Since this value is near the approximate diameter of Ananke itself, it is likely the parent body was not heavily disrupted.<ref>{{cite journal |last1=Sheppard |first1=Scott S. |author-link=Scott S. Sheppard |last2=Jewitt |first2=David C. |author-link2=David C. Jewitt |date=May 5, 2003 |title=An abundant population of small irregular satellites around Jupiter |url=http://www.ifa.hawaii.edu/~jewitt/papers/JSATS/SJ2003.pdf |journal=Nature |volume=423 |issue=6937 |pages=261–263 |bibcode=2003Natur.423..261S |doi=10.1038/nature01584 |pmid=12748634 |s2cid=4424447 |archive-url=https://web.archive.org/web/20060813235622/http://www.ifa.hawaii.edu/~jewitt/papers/JSATS/SJ2003.pdf |archive-date=August 13, 2006}}
</ref> 

Available photometric studies put this in doubt, however, and suggest that [[secular resonance]] has mixed the Ananke and Pasiphae groups: three of the moons of the former family ([[Harpalyke (moon)|Harpalyke]], [[Praxidike (moon)|Praxidike]] and [[Iocaste (moon)|Iocaste]]) display similar grey colours (average [[color index|colour indices]]:  B−V = 0.77 and V−R = 0.42) while Ananke itself is on the boundary between grey and light red.<ref name="Grav2003">
{{Cite journal |last1=Grav |first1=Tommy |last2=Holman |first2=Matthew J. |author-link2=Matthew J. Holman |last3=Gladman |first3=Brett |author-link3=Brett Gladman |last4=Aksnes |first4=Kaare |author-link4=Kaare Aksnes |date=2003-01-02 |title=Photometric Survey of the Irregular Satellites |journal=[[Icarus (journal)|Icarus]] |language=en |volume=166 |issue=1 |pages=33–45 |doi=10.1016/j.icarus.2003.07.005 |arxiv=astro-ph/0301016 |bibcode=2003Icar..166...33G |s2cid=7793999 }}</ref>

[[Image:TheIrregulars JUPITER Ananke CORE.svg|thumb|left|300px|This diagram compares the orbital elements and relative sizes of the core members of the Ananke group. The horizontal axis illustrates their average distance from Jupiter, the vertical axis their orbital inclination, and the circles their relative sizes.]]
[[Image:TheIrregulars JUPITER Ananke.svg|thumb|right|300px|This diagram offers a wider field of view than the previous one, showing other small satellites clustered near the core Ananke group. ([[Philophrosyne (moon)|Philophrosyne]] and [[Eurydome (moon)|Eurydome]] were thought to be Ananke group members when this diagram was produced; they turned out to be [[Pasiphae group]] members.)]]{{Clear}}