{{Use dmy dates|date=February 2026}} {{Short description|Group of retrograde irregular satellites of Jupiter}} [[File:Ananke group aei orbits polar plot.svg|thumb|upright=1.5|This diagram compares the [[orbital elements]] and relative sizes of the known members of the Ananke group {{asof|April 2026|lc=y}}. The horizontal axis illustrates their average distance from Jupiter, the vertical axis their orbital inclination, and the circles their relative sizes.]] [[File:Jupiter irregular moons polar plot.svg|thumb|upright=1.5|107 irregular moons of Jupiter plotted by semi-major axis and inclination {{asof|April 2026|lc=y}}. The Ananke group is shown as a tight cluster of yellow-colored points on the left.]]
The '''Ananke group''' (or ''family'' or ''cluster'') is a group of [[Retrograde motion|retrograde]] [[irregular satellite]]s of [[Jupiter]] that follow similar [[orbit]]s to [[Ananke (moon)|Ananke]] and are thought to have a common origin.
Their [[semi-major axis|semi-major axes]] (distances from Jupiter) range between 19.2 and 21.8 million km, their [[orbital inclination]]s between 144.3° and 155.5°, and their [[Orbital eccentricity|orbital eccentricities]] between 0.09 and 0.30.
The [[International Astronomical Union]] (IAU) reserves names ending in '''-e''' for all retrograde moons of Jupiter, 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 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 million km 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.<ref name="Nesvorny2003"/>
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.<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 group|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"/>
==Classification== The Ananke group is typically simply visually identified in orbital element space, differing in inclination from the [[Carme group]] and having smaller semi-major axes than the Pasiphae group. However, some authors only consider the tight cluster immediately surrounding Ananke to be part of its group.<ref name="Nesvorny2003"/><ref name="Nesvorny2004"/><ref name="Brozović&Jacobson2017">{{Cite journal |last=Brozović |first=Marina |last2=Jacobson |first2=Robert A. |date=2017-04-01 |title=The Orbits of Jupiter’s Irregular Satellites |journal=The Astronomical Journal |volume=153 |issue=4 |pages=147 |bibcode=2017AJ....153..147B |doi=10.3847/1538-3881/aa5e4d |issn=0004-6256 |doi-access=free}}</ref> At other times, there is no distinction made between the Ananke and Pasiphae groups, and the two may be considered a single group.<ref name="Grav2003"/><ref>{{Cite journal |last=Grav |first=T. |last2=Bauer |first2=J. M. |last3=Mainzer |first3=A. K. |last4=Masiero |first4=J. R. |last5=Nugent |first5=C. R. |last6=Cutri |first6=R. M. |last7=Sonnett |first7=S. |last8=Kramer |first8=E. |date=2015-08-04 |title=NEOWISE: OBSERVATIONS OF THE IRREGULAR SATELLITES OF JUPITER AND SATURN |url=https://iopscience.iop.org/article/10.1088/0004-637X/809/1/3 |journal=The Astrophysical Journal |volume=809 |issue=1 |pages=3 |arxiv=1505.07820 |bibcode=2015ApJ...809....3G |doi=10.1088/0004-637X/809/1/3 |issn=1538-4357 |s2cid=5834661 |doi-access=free}}</ref><ref name="Vilas & Hendrix 2024">{{Cite journal |last=Vilas |first=Faith |last2=Hendrix |first2=Amanda R. |date=2024-02-01 |title=Clues to the Origin of Jovian Outer Irregular Satellites from Reflectance Spectra |url=https://iopscience.iop.org/article/10.3847/PSJ/ad150b |journal=The Planetary Science Journal |volume=5 |issue=2 |pages=34 |bibcode=2024PSJ.....5...34V |doi=10.3847/PSJ/ad150b |issn=2632-3338 |s2cid=267531422 |doi-access=free}}</ref>
==List== The members of the Ananke group are (in order of date announcement):<ref name="SheppardJewittPorco2004">{{cite book |last1=Sheppard |first1=Scott S. |author-link1=Scott S. Sheppard |url= |title=Jupiter. The planet, satellites and magnetosphere. |last2=Jewitt |first2=David C. |author-link2=David Jewitt |last3=Porco |first3=Carolyn |author-link3=Carolyn Porco |publisher=[[Cambridge University Press]] |year=2004 |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 |chapter=Jupiter's outer satellites and Trojans |editor2=Dowling |editor-first2=Timothy E. |editor3=McKinnon |editor-first3=William B. |chapter-url=http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf |archive-url=https://web.archive.org/web/20070614045102/http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf |archive-date=2007-06-14|bibcode=2004jpsm.book..263J|s2cid=117582048}}</ref><ref name="Nesvorny2004"/><!-- please read the comment on the talk page before modifying this list --> {| class="wikitable sortable" style="text-align:center;" !Name||Diameter<BR>(km)<ref name="scott jupiter"/>||Semi-Major Axis<BR>(km)||Period<BR>(days)<ref name="nasa parameters"/>{{Efn|Negative period is indicative of retrograde motion.}} |-id=Ananke |[[Ananke (moon)|Ananke]] || 28 || {{val|21029500}} || –623.11 |-id=Iocaste <!-- S/2000 J 3 --> |[[Iocaste (moon)|Iocaste]] || 5 || {{val|21062300}} || –624.55 |-id=Harpalyke <!-- S/2000 J 5 --> |[[Harpalyke (moon)|Harpalyke]] || 4 || {{val|20887500}} || –616.78 |-id=Praxidike <!-- S/2000 J 7 --> |[[Praxidike (moon)|Praxidike]] || 7 || {{val|20931100}} || –618.72 |-id=Thyone <!-- S/2001 J 2 --> |[[Thyone (moon)|Thyone]] || 4 || {{val|20972700}} || –620.59 |-id=Hermippe <!-- S/2001 J 3 --> |[[Hermippe (moon)|Hermippe]] || 4 || {{val|21103600}} || –626.38 |-id=Euanthe <!-- S/2001 J 7 --> |[[Euanthe (moon)|Euanthe]] || 3 || {{val|20822900}} || –613.93 |-id=Orthosie <!-- S/2001 J 9 --> |[[Orthosie (moon)|Orthosie]] || 2 || {{val|20897800}} || –617.23 |-id=Euporie <!-- S/2001 J 10 --> |[[Euporie (moon)|Euporie]] || 2 || {{val|19261900}} || –546.18 |-id=S/2003 J 2 |[[S/2003 J 2]] || 2 || {{val|20992900}} || –621.47 |-id=Eupheme <!-- S/2003 J 3 --> |[[Eupheme (moon)|Eupheme]] || 2 || {{val|20763400}} || –611.32 |-id=Helike <!-- S/2003 J 6 --> |[[Helike (moon)|Helike]] || 4 || {{val|20911400}} || –617.86 |-id=S/2003 J 12 |[[S/2003 J 12]] || 1 || {{val|20959300}} || –619.96 |-id=S/2003 J 16 |[[S/2003 J 16]] || 2 || {{val|20877500}} || –622.88 |-id=S/2003 J 18 |[[S/2003 J 18]] || 2 || {{val|20332800}} || –592.33 |-id=Mneme <!-- S/2003 J 21 --> |[[Mneme (moon)|Mneme]] || 2 || {{val|20815800}} || –613.61 |-id=Thelxinoe <!-- S/2003 J 22 --> |[[Thelxinoe (moon)|Thelxinoe]] || 2 || {{val|20972300}} || –620.55 |-id=S/2010 J 2 |[[S/2010 J 2]] || 1 || {{val|20786900}} || –612.35 |-id=S/2016 J 1 |[[S/2016 J 1]] || 1 || {{val|20796700}} || –612.78 |-id=S/2017 J 3 |[[S/2017 J 3]] || 2 || {{val|20936500}} || –618.97 |-id=S/2017 J 7 |[[S/2017 J 7]] || 2 || {{val|20960400}} || –620.02 |-id=S/2017 J 9 |[[S/2017 J 9]] || 3 || {{val|21764200}} || –656.05 |-id=S/2021 J 1 |S/2021 J 1 || 1 || {{val|20954700}} || –619.77 |-id=S/2021 J 2 |S/2021 J 2 || 1 || {{val|20926600}} || –618.50 |-id=S/2021 J 3 |S/2021 J 3 || 2 || {{val|20776600}} || –611.87 |-id=S/2022 J 3 |S/2022 J 3 || 1 || {{val|21015100}} || –622.44 |-id=S/2017 J 10 |S/2017 J 10 || 2 || {{val|21075800}} || –625.15 |-id=S/2010 J 6 |S/2010 J 6 || 2 || {{val|21489800}} || –643.67 |-id=S/2021 J 8 |S/2021 J 8 || 1 || {{val|20978900}} || –620.85 |}
== Notes == <references group="lower-alpha" />
==References== {{Reflist|refs=
<ref name="nasa parameters">{{cite web |title = Planetary Satellite Mean Elements |url = https://ssd.jpl.nasa.gov/sats/elem/ |work = Jet Propulsion Laboratory |publisher = California Institute of Technology |date = 25 January 2024}}</ref>
<ref name="Grav2003">{{Cite journal |last1=Grav |first1=Tommy |author-link=Tommy Grav |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>
<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|journal=[[The Astronomical Journal]] |volume=126 |issue=1 |pages=398–429|doi=10.1086/375461 |bibcode=2003AJ....126..398N |s2cid=8502734 |doi-access=free }}</ref>
<ref name="Nesvorny2004">{{Cite journal |last1=Nesvorný |first1=David |last2=Beaugé |first2=Cristian |last3=Dones |first3=Luke |date=2004 |title=Collisional Origin of Families of Irregular Satellites |journal=[[The Astronomical Journal]] |volume=127 |issue=3 |pages=1768–1783 |bibcode=2004AJ....127.1768N |doi=10.1086/382099 |s2cid=27293848 |via=[[IOP Publishing]]|doi-access=free }}</ref>
<ref name="scott jupiter">{{cite web |title = Moons of Jupiter |url = https://sites.google.com/carnegiescience.edu/sheppard/moons/jupitermoons |work = Earth & Planets Laboratory |publisher = Carnegie Institution for Science |date = 25 January 2024}}</ref>
}}
==External links== {{Moons of Jupiter}}
[[Category:Ananke group]] [[Category:Moons of Jupiter]] [[Category:Irregular satellites]] [[Category:Moons with a retrograde orbit]]