Physical Propertiesand Color Variegation of 243 Ida

Kurzfassung

The asteroid 243 Ida will be the second fly-by target of the Galileo space probe. During the 1990 and 1991 apparitions, we performed CCDphotometry and spectrophotometry of ths S-type asteroid in order to determine its physical and dynamical properties. The measurements were performed with the DLR CCD-cameraat the observa- tories of Loiano (Italy) and ESO (La Silla, Chile). During these observations we obtained composite lightcurves in V-Johnson band, which we used to derived the magnitude-phase and the amlpitude-phase relation-ships. Rotational lightcurves were also acquired with spectral filters at 700nm and 950nm, representing respectively wavelengths near the maximum of the Ida relfection spectrum and the olivine-pyroxene absorption band. These measurements have revealed a significant variation of the 1-mm absorption of about 4% at a detection level of 3s. The observed variegation indicates a heterogeneous surface of 243 Ida, and is similar to the variations we detected which our observations of 951 Gaspra, which have been successively confirmed by the images returned by Galileo. We will perform additional observations of 243 Ida during its next opposition in 1993. the new results will also be presented at the meeting.