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Ananke group

Topic: Astronomy

 From HandWiki - Reading time: 6 min

Short description: Group of retrograde irregular satellites of Jupiter
This diagram compares the orbital elements and relative sizes of the known members of the Ananke group as of April 2026. The horizontal axis illustrates their average distance from Jupiter, the vertical axis their orbital inclination, and the circles their relative sizes.
107 irregular moons of Jupiter plotted by semi-major axis and inclination as of April 2026. 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 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 million km, their orbital inclinations between 144.3° and 155.5°, and their 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 of the mean orbital parameters[lower-alpha 1] 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.[1]

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.[2]

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.[3]

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.[1][4][5] At other times, there is no distinction made between the Ananke and Pasiphae groups, and the two may be considered a single group.[3][6][7]

List

The members of the Ananke group are (in order of date announcement):[8][4]

Name Diameter
(km)[9]		 Semi-Major Axis
(km)		 Period
(days)[10][lower-alpha 2]
Ananke 28 21029500 –623.11
Iocaste 5 21062300 –624.55
Harpalyke 4 20887500 –616.78
Praxidike 7 20931100 –618.72
Thyone 4 20972700 –620.59
Hermippe 4 21103600 –626.38
Euanthe 3 20822900 –613.93
Orthosie 2 20897800 –617.23
Euporie 2 19261900 –546.18
S/2003 J 2 2 20992900 –621.47
Eupheme 2 20763400 –611.32
Helike 4 20911400 –617.86
S/2003 J 12 1 20959300 –619.96
S/2003 J 16 2 20877500 –622.88
S/2003 J 18 2 20332800 –592.33
Mneme 2 20815800 –613.61
Thelxinoe 2 20972300 –620.55
S/2010 J 2 1 20786900 –612.35
S/2016 J 1 1 20796700 –612.78
S/2017 J 3 2 20936500 –618.97
S/2017 J 7 2 20960400 –620.02
S/2017 J 9 3 21764200 –656.05
S/2021 J 1 1 20954700 –619.77
S/2021 J 2 1 20926600 –618.50
S/2021 J 3 2 20776600 –611.87
S/2022 J 3 1 21015100 –622.44
S/2017 J 10 2 21075800 –625.15
S/2010 J 6 2 21489800 –643.67
S/2021 J 8 1 20978900 –620.85

Notes

  1. ↑ 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 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.
  2. ↑ Negative period is indicative of retrograde motion.

References

  1. ↑ 1.0 1.1 Nesvorný, David; Alvarellos, Jose L. A.; Dones, Luke; Levison, Harold F. (July 2003). "Orbital and Collisional Evolution of the Irregular Satellites". The Astronomical Journal 126 (1): 398–429. doi:10.1086/375461. Bibcode: 2003AJ....126..398N. 
  2. ↑ Sheppard, Scott S.; Jewitt, David C. (May 5, 2003). "An abundant population of small irregular satellites around Jupiter". Nature 423 (6937): 261–263. doi:10.1038/nature01584. PMID 12748634. Bibcode: 2003Natur.423..261S. http://www.ifa.hawaii.edu/~jewitt/papers/JSATS/SJ2003.pdf. 
  3. ↑ 3.0 3.1 Grav, Tommy; Holman, Matthew J.; Gladman, Brett; Aksnes, Kaare (2003-01-02). "Photometric Survey of the Irregular Satellites" (in en). Icarus 166 (1): 33–45. doi:10.1016/j.icarus.2003.07.005. Bibcode: 2003Icar..166...33G. 
  4. ↑ 4.0 4.1 Nesvorný, David; Beaugé, Cristian; Dones, Luke (2004). "Collisional Origin of Families of Irregular Satellites". The Astronomical Journal 127 (3): 1768–1783. doi:10.1086/382099. Bibcode: 2004AJ....127.1768N. 
  5. ↑ Brozović, Marina; Jacobson, Robert A. (2017-04-01). "The Orbits of Jupiter’s Irregular Satellites". The Astronomical Journal 153 (4): 147. doi:10.3847/1538-3881/aa5e4d. ISSN 0004-6256. Bibcode: 2017AJ....153..147B. 
  6. ↑ Grav, T.; Bauer, J. M.; Mainzer, A. K.; Masiero, J. R.; Nugent, C. R.; Cutri, R. M.; Sonnett, S.; Kramer, E. (2015-08-04). "NEOWISE: OBSERVATIONS OF THE IRREGULAR SATELLITES OF JUPITER AND SATURN". The Astrophysical Journal 809 (1): 3. doi:10.1088/0004-637X/809/1/3. ISSN 1538-4357. Bibcode: 2015ApJ...809....3G. https://iopscience.iop.org/article/10.1088/0004-637X/809/1/3. 
  7. ↑ Vilas, Faith; Hendrix, Amanda R. (2024-02-01). "Clues to the Origin of Jovian Outer Irregular Satellites from Reflectance Spectra". The Planetary Science Journal 5 (2): 34. doi:10.3847/PSJ/ad150b. ISSN 2632-3338. Bibcode: 2024PSJ.....5...34V. https://iopscience.iop.org/article/10.3847/PSJ/ad150b. 
  8. ↑ Sheppard, Scott S.; Jewitt, David C.; Porco, Carolyn (2004). "Jupiter's outer satellites and Trojans". in Bagenal, Fran. Jupiter. The planet, satellites and magnetosphere.. Cambridge planetary science. 1. Cambridge, UK: Cambridge University Press. pp. 263–280. ISBN 0-521-81808-7. Bibcode: 2004jpsm.book..263J. http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf. 
  9. ↑ "Moons of Jupiter". Earth & Planets Laboratory. Carnegie Institution for Science. 25 January 2024. https://sites.google.com/carnegiescience.edu/sheppard/moons/jupitermoons. 
  10. ↑ "Planetary Satellite Mean Elements". Jet Propulsion Laboratory. California Institute of Technology. 25 January 2024. https://ssd.jpl.nasa.gov/sats/elem/. 



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