Dactyl (moon)

(243) Ida I Dactyl (pronEng|ˈdæktɨl "dak'-tl") 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, but two main hypotheses exist. The first is that Dactyl and Ida formed at the same time, and the second is that Dactyl 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.

ee also

*List of geological features on 243 Ida and Dactyl

External links

* [http://www.nineplanets.org/ida.html 243 Ida and Dactyl] from "The Nine8 Planets"
* [http://www.solarviews.com/eng/ida.htm Asteroid Ida and Dactyl] from "Views of the Solar System"
* [http://www.cfa.harvard.edu/iauc/05900/05948.html IAUC 5948] announcing Dactyl's discovery
* [http://www.cfa.harvard.edu/iauc/06000/06082.html#Item2 IAUC 6082] announcing Dactyl's naming
* [http://near.jhuapl.edu/Voyage/img/Ida_dactyl.gifIda and Dactyl] in false coloring, to reveal surface differences