Ananke group facts for kids

The Ananke group is a family of moons that orbit the giant planet Jupiter. These moons are special because they move in a "backwards" direction compared to Jupiter's spin. Scientists call this retrograde motion. Also, these moons are not perfectly round like Earth's Moon; they are non-spherical, meaning they have irregular shapes.

All the moons in the Ananke group follow very similar paths around Jupiter, almost like they are part of the same cosmic dance. This suggests they might have all come from the same original object. Their distances from Jupiter range from about 19.3 million to 22.7 million kilometers. Their orbits are also tilted quite a bit, between 145.7 and 154.8 degrees, and they are not perfectly circular.

This diagram illustrates the largest irregular satellites of Jupiter. The location of the Ananke group is illustrated by Ananke's presence near the bottom. An object's position on the horizontal axis indicates its distance from Jupiter. The vertical axis indicates its inclination. 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 main members of this group, listed from the largest to the smallest, include:

• Ananke
• Praxidike
• Iocaste
• Harpalyke
• Thyone
• Euanthe
• Euporie

The International Astronomical Union (IAU) is the group that names planets and moons. They have a rule that all moons moving in a retrograde (backwards) orbit, like those in the Ananke group, must have names that end with the letter -e.

How the Ananke Group Formed

Scientists believe the Ananke group formed a long, long time ago. They think a large space rock, called an asteroid, was pulled in by Jupiter's strong gravity. Once it was captured, this asteroid likely crashed into something else or broke apart on its own. This big break-up then created all the smaller moons we see today in the Ananke group.

Based on how big these moons are now, the original asteroid might have been about 28 kilometers (about 17 miles) wide. Since Ananke itself is close to that size, it seems the original asteroid didn't completely shatter into tiny pieces. Instead, it probably broke into a few large chunks and many smaller ones.

Interestingly, three of the moons in this family – Harpalyke, Praxidike, and Iocaste – all look similar with a grey color. Ananke itself is a bit different, appearing somewhere between grey and a light red. This slight color difference might give clues about how they formed.

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.

This diagram offers a wider view than the previous one, showing other small moons clustered near the core Ananke group.

See also

In Spanish: Grupo de Ananké para niños