Is it true that only planets have moons?
Can asteroids have moons?
Yes, asteroids can have moons! Some of the larger asteroids in our Solar System actually do have moons. In 1993, an tiny moon called Dactyl was discovered orbiting the large asteroid Ida. Dactyl is only about 1 mile wide, while Ida is about 19 miles across. Since then, several other moons have been discovered orbiting asteroids.
In 1999, an 8 mile wide moon called Petit-Prince was discovered orbiting the 135 mile wide asteroid Eugenia. In 2000, the 90 mile wide asteroid Pulcova was discovered to have its own moon, about nine miles wide. Over two dozen more have been discovered.
http://coolcosmos.ipac.caltech.edu/ask/187-Can-asteroids-have-moons-