Ananke group

{{Short description|Group of retrograde irregular satellites of Jupiter}}Image:TheIrregulars JUPITER GROUPS.svg. Eccentricity is indicated by yellow bars illustrating the object's maximum and minimum distances from Jupiter. Circles illustrate an object's size in comparison to the others.]]

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 19.2 and 21.8 Gm, their orbital inclinations between 144.3° and 155.5°, and their orbital eccentricities between 0.09 and 0.30.

The members of the Ananke group are:{{Cite book |last1=Jewitt |first1=David C. |url=http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf |title=Jupiter. The planet, satellites, and magnetosphere |last2=Sheppard |first2=Scott S. |last3=Porco |first3=Carolyn |date=2004 |publisher=Cambridge University Press |isbn=0-521-81808-7 |editor-last=Bagenal |editor-first=Fran |editor-link=Fran Bagenal |series=Cambridge planetary science |volume=1 |location=Cambridge, UK |pages=263–280 |author-link=David C. Jewitt |author-link2=Scott S. Sheppard |author-link3=Carolyn Porco |editor2-last=Dowling |editor2-first=Timothy E. |editor3-last=McKinnon |editor3-first=William B. |archive-url=https://web.archive.org/web/20070614045102/http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf |archive-date=2007-06-14 |department=Jupiter's outer satellites and Trojans}}{{Cite journal |last1=Nesvorný |first1=David |last2=Beaugé |first2=Cristian |last3=Dones |first3=Luke |date=2004 |title=Collisional Origin of Families of Irregular Satellites |url=https://iopscience.iop.org/article/10.1086/382099/pdf |journal=The Astronomical Journal |volume=127 |issue=3 |pages=1768–1783 |bibcode=2004AJ....127.1768N |doi=10.1086/382099 |s2cid=27293848 |via=IOP Publishing}}

class="wikitable sortable" style="text-align:center;" !Name	Diameter (km)	Period (days){{Efn\|Negative period is indicative of retrograde motion.}}
id=Ananke \|Ananke	28	–629.79
id=Harpalyke \|Harpalyke	4	–623.32
id=Iocaste \|Iocaste	5	–631.59
id=Praxidike \|Praxidike	7	–625.39
id=Thyone \|Thyone	4	–627.18
id=Hermippe \|Hermippe	4	–633.90
id=Euanthe \|Euanthe	3	–620.44
id=Euporie \|Euporie	2	–550.69
id=Orthosie \|Orthosie	2	–622.59
id=Mneme \|Mneme	2	–620.07
id=Thelxinoe \|Thelxinoe	2	–628.03
id=Helike \|Helike	4	–626.33
id=S/2010 J 2 \|S/2010 J 2	1	–618.84
id=S/2016 J 1 \|S/2016 J 1	1	–618.49
id=S/2003 J 18 \|S/2003 J 18	2	–598.12
id=Eupheme \|Eupheme	2	–617.73
id=S/2017 J 3 \|S/2017 J 3	2	–625.60
id=S/2017 J 7 \|S/2017 J 7	2	–626.56
id=S/2017 J 9 \|S/2017 J 9	3	–666.11
id=S/2017 J 10 \|S/2017 J 10	2	–645.09
id=S/2003 J 2 \|S/2003 J 2	2	–628.79
id=S/2003 J 12 \|S/2003 J 12	1	–627.24
id=S/2003 J 16 \|S/2003 J 16	2	–622.88
id=S/2021 J 1 \|S/2021 J 1	1	–627.14
id=S/2021 J 2 \|S/2021 J 2	1	–625.14
id=S/2021 J 3 \|S/2021 J 3	2	–618.33
id=S/2022 J 3 \|S/2022 J 3	1	–630.67

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 mean orbital parameters{{Efn|Osculating orbital parameters of irregular satellites of Jupiter change widely in short intervals due to heavy 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 m/s), compatible with a single collision and breakup.{{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 }}

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 |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}}

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, 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.

{{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 |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 }}

Image:TheIrregulars JUPITER Ananke CORE.svg

Image:TheIrregulars JUPITER Ananke.svg and Eurydome were thought to be Ananke group members when this diagram was produced; they turned out to be Pasiphae group members.)]]{{Clear}}