Up until 1995, moonlets were only hypothetical components of Saturn's F-ring structure, when the Earth passed through Saturn's ring plane. The Hubble Space Telescope and the European Southern Observatory both captured objects orbiting close or near the F-ring. In 2004, Cassini caught an object 4–5 kilometers in diameter on the outer ring of the F-ring and then 5 hours later on the inner F-ring, showing that the object had orbited.
Three different types of small moons have been called moonlets:
- A belt of objects embedded in a planetary ring, especially around Saturn, such as those in the A Ring, S/2009 S 1 in the B Ring ("propeller" moonlets), and those in the F Ring
- Occasionally asteroid moons, such as those of 87 Sylvia
- Flashes seen near Jupiter's moon Amalthea that is likely debris ejected from its surface