Asteroid 243, discovered in 1884 by the Austrian astronomer Johann Palisa (1848–1925). It has a satellite, Dactyl. Ida, an S-class asteroid, measures 54 × 24 × 15 km and rotates in a period of 4.6 hours about its shortest axis. It is a member of the Koronis family. If its parent body was broken into several pieces, one of these fragments may have become its satellite. Its orbit has a semimajor axis of 2.863 AU, period 4.84 years, perihelion 2.74 AU, aphelion 2.98 AU, and inclination 1°.1.
Subjects: Astronomy and Astrophysics.