The flyby of 243 Ida occurred 28 August, 1993. Preliminary results
from 3
of the data acquired by the SSI have been published
[ Belton et al., 1994] and preliminary results
from the NIMS reported [ Carlson et al., 1994].
The large scale surface features of Ida (Figure 4) have been
summarized by Belton et al., [1994]
and compared with those of Gaspra [ Chapman, 1994].
243 Ida is irregularly shaped with dimensions of 
km, more than twice as big as Gaspra in linear
dimensions. Its rotation is retrograde, opposite to that of
Gaspra, and its spin period, 4.633 hr, is more than twice as fast
as that of Gaspra. Craters and large planar features are
identified and can be as large as 100-150 m across. These are most
likely to be the largest remnants retained on the asteroid of
impact ejecta, and the largest constituent of the regolith.
Blocks were not seen on Gaspra. Linear features, systems of
grooves, albedo stripes, and short crater chains are common on Ida.
The grooves show no preferred orientation with respect to local
slopes and some grooves intersect craters. Their origin
could be attributable to boulder movement, or they could be a
surface expression of global stresses imposed on the bedrock
resulting from large crater impacts.
An interesting difference between Ida and Gaspra is the size-frequency distribution of craters. Ida is the most densely cratered body in the solar system [ Chapman, 1994]. The density of craters is similar to a saturated surface where the crater size frequency follows a power law distribution with slope of -3 and crater morphologies ranging from fresh (young) to degraded (old). With a surface in cratered equilibrium, it is not possible to extract the production mechanism uniquely. The crater population on Ida could be produced by the same crater flux hypothesized for Gaspra but active 10 times longer, according to Chapman, [1994]. The surface of Ida could date back to the period of Late Heavy Bombardment, a period in the formation of the solar system dating back over 4 billion years. This is a surprising finding, as Ida is a member of the Koronis family of asteroids which presumably formed from a major collision after the end of the Late Heavy Bombardment era.