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:[1] [2]
| Name | Diameter (km) | Period (days) | |
|---|---|---|---|
| 28 | –629.79 | ||
| 4 | –623.32 | ||
| 5 | –631.59 | ||
| 7 | –625.39 | ||
| 4 | –627.18 | ||
| 4 | –633.90 | ||
| 3 | –620.44 | ||
| 2 | –550.69 | ||
| 2 | –622.59 | ||
| 2 | –620.07 | ||
| 2 | –628.03 | ||
| 4 | –626.33 | ||
| 1 | –618.84 | ||
| 1 | –618.49 | ||
| 2 | –598.12 | ||
| 2 | –617.73 | ||
| 2 | –625.60 | ||
| 2 | –626.56 | ||
| 3 | –666.11 | ||
| 2 | –628.79 | ||
| 1 | –627.24 | ||
| 2 | –622.88 | ||
| 1 | –627.14 | ||
| 1 | –625.14 | ||
| 2 | –618.33 | ||
| 1 | –630.67 |
The International Astronomical Union (IAU) reserves names ending in -e for all retrograde moons, including this group's members.
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 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.[3]
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.[4]
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.[5]