(243) Ida I Dactyl is a tiny asteroid moon (diameter 1.4 km) that orbits asteroid 243 Ida. It was imaged by the Galileo spacecraft on August 28, 1993; the Galileo mission member Ann Harch, while examining the delayed image downloads, discovered it on February 17, 1994. It was provisionally designated S/1993 (243) 1. The satellite was named after the mythical creatures called dactyls who lived on the Mount Ida according to the Greek mythology.

Dactyl orbits Ida with a period of 1.54 days at an average distance of 108 km, with an inclination of 9° to Ida's equator. The orbit is not very accurately known because Galileo coincidentally passed very nearly in its plane while taking the images.

The origins of Dactyl are unclear. The two main hypotheses are that it and Ida formed at the same time, and that it was knocked loose by a later impact. Both hypotheses have problems and cannot explain the situation satisfactorily.

Dactyl was the first asteroid moon discovered. The discovery settled the long debate over the existence of asteroid moons.

See also

• List of geological features on 243 Ida and Dactyl

External links

• 243 Ida and Dactyl from The Nine Planets
• Asteroid Ida and Dactyl from Views of the Solar System
• IAUC 5948 announcing Dactyl's discovery
• IAUC 6082 announcing Dactyl's naming

Dactyl (Asteroid) | 다크틸 | Dactyl | Asteroidemånen Dactyl | 243 Daktyl