The objective of this and a companion ISO proposal (Search for
Hydrated Minerals Around O-rich Red Supergiants) is to investigate the
origin of preterrestrial hydrated silicates in a broad cosmochemical
context.  Here we propose to acquire the best high resolution, near-IR
spectra of the two largest asteroids (1 Ceres and 2 Pallas) to permit
detailed spectrochemical analyses of trace volatile components in
their surface minerals.  In order to place their detailed mineralogy
into a broader context, we also propose to acquire moderate resolution
observations of smaller objects in Ceres' spectral class and hydrated
asteroids assigned to other spectral classes.  The results may reveal
the identity of the original nebular condensates and their possible
links to interstellar grain compositions.  The spectra needed for
this study cannot be obtained at the best ground-based and airborne
observatories because of interference from telluric absorptions.
Only ISO provides an unobstructed view of the 2.4-4.0 micron spectral
region at sufficient resolving power and signal-to-noise ratio (SNR)
to reveal all diagnostic spectral features that can possibly be
obtained in remote observations.