Dactyl moon around an Asteroid
Asteroids are dry, dusty lumps of rock that failed to make a rocky planet. There are 100,000 larger than about 12.5 miles (20km) across. As size diminishes, the quantity increases. Most orbit the Sun between Mars and Jupiter.
Dactyl is a rare asteroid. It is the moon of another asteroid named Ida. Ida is 37 miles (60km) long and shows signs of past collisions. Ida journeys around the sun every 4.8 years. Dactyl is just 1 mile (1.6km) long and it orbits Ida every 27 hours. It's density is 2.6 to 0.5 g/cm. For these reason so far nobody has journeyed to these points.
Dactyl was discovered by Johann Palisa. It was discovered on September 29, 1884.
Ida and dactyl are thought to have been created at the same time, from the disruption of Koronis parent body.