simulations, Dactyl's pericenter must be more than about from Ida for it to remain in a stable orbit. The range of orbits generated by the simulations was narrowed down by the necessity of having the orbits pass through points at which Galileo observed Dactyl to be at 16:52:05 UT on 28 August 1993, about from Ida at longitude 85°. On 26 April 1994, the Hubble Space Telescope observed Ida for eight hours and was unable to spot Dactyl. It would have been able to observe it if it were more than about from Ida. If in a circular orbit at the distance at which it was seen, Dactyl's orbital period would be about 20 hours. Its orbital speed is roughly , "about the speed of a fast run or a slowly thrown baseball". Age and origin Dactyl may have originated at the same time as Ida, from the disruption of the Koronis parent body. However, it may have formed more recently, perhaps as ejecta from a large impact on Ida. It is extremely unlikely that it was captured by Ida. Dactyl may have suffered a major impact around 100 million years ago, which reduced its size. See also List of geological features on 243 Ida and Dactyl List of minor planets Notes References Journal articles Books Other Alt URL External links Asteroids with Satellites, Robert Johnston, johnstonsarchive.net Koronis asteroids Ida Ida Binary asteroids 19980823 243 Ida S-type asteroids (Tholen) S-type asteroids (SMASS) 18840929