Discovered in 1995 by the Galileo spacecraft, Dactyl is a moon, less than a mile in diameter, of the potato shaped asteroid Ida.
It was the first moon discovered orbiting an asteroid. Scientist are unsure if the tiny moon is a piece that broke off of the asteroid, or if it was captured by the asteroid. It was the first evidence scientist had that asteroids had satellites. Since its discovery, over two dozen moons have been discovered orbiting asteroids.