Physical study of the asteroid 243 Ida, second fly-by target of the Galileo spacecraft.

Abstract

According to the present mission planning, 243 Ida will be the secondmain belt asteroid to be encountered by the Galileo spacecraft, the fly-by being scheduled for August, 1993. In the framework of our observation program of space mission targets, we have undertaken CCD and photoelectric measurements of 243 Ida in the B and V Johnson bands from the observatories of Loiano (Italy) and ESO (La Silla, Chile) at the time of its 1990 apparition. From seven observations which spanned a period of three month in timeand a phase angle range from about 4 to 20 degrees, we obtain three composite lightcurves of this asteroid. The good quality of these datas allows a substantial improvement in the determination of the synodic rotational period of 243 Ida, which results to be Psyn&#61 4.6330+-0.0005 hr. We derive for the first time the magnitude-phase relationship and an estimation for the amplitude-phase relationship (APR) of this asteroid. The computation of the parametersof the Bowell-Harris-Lumme relation from our measurements gives: H&#6110.042+-0.008 mag and G&#610.15+-0.02 mag deg-1. From the lightcurve amplitude-phase relation we estimate s (APR)&#610.010 mag deg-1 and m&#610.016 deg-1. We also derive the color index B-V&#610.87+-0.03.