Dozens of new moons around these planets have recently been discovered. Saturn has 30 moons, Jupiter 28, Uranus 21, and Neptune has 8. A dozen new kilometre sized satellites were gleaned from observations of Saturn. These discoveries came from ground based instruments, complementing spacecraft measurements that could not efficiently search for satellites more remote to the planet. Around Saturn are both prograde and retrograde orbits. Retrograde moons circle anticlockwise, and prograde moons circle clockwise. The mechanism of satellite capture remain an outstanding problem in planetary science.

Nature/volume 412/ 12^th July 2001, p.133.