Many Retrograde Orbit Satellites around Jupiter and Saturn have been found recently. Most of them are small with irregular shapes. They are farther from the planet than regular satellites. Their orbits have big eccetricities.

We tested their dynamical origin and found:

1. 1. The small bodies can be captured by normal satellites and form retrograde orbits. But these orbits are not stable. Sooner or later, they would escape from planetary region or fall down into the planets.

2. 2. Another way is that they have formed by collisions just after regular moons formed. We studied the mechanism and obtained good results.