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 kilometers and with a relative velocity of 12.4 kilometers per second. 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|