Ida, imaged by the Galileo spacecraft as it flew by in 1994.
On August 28, 1993, Ida became the second asteroid, after Gaspra, to be encountered by a spacecraft when Galileo flew past it at a distance of 2,400 km and with a relative velocity of 12.4 km/s. The highlight of the flyby was the discovery (made in February 1994 when images stored on the spacecraft's tape recorder were finally transmitted to Earth) that Ida has a satellite, subsequently christened Dactyl. Ida's age is a puzzle. Its surface is heavily cratered suggesting that it has existed in its present form for at least a billion years, which predates estimates for the Koronis breakup.
|size||56 × 24 × 21 km|
|rotational period||4.63 hours|
|semimajor axis||2.861 AU|