The objective of this and a companion ISO proposal (Spectroscopic
Studies of Volatile-rich Asteroids) is to investigate the origin of
preterrestrial hydrated silicates in a broad cosmochemical context.
Here we propose to follow up on the unexpected detection of the
2.7-micron hydrate absorption band in circumstellar dust around SN
1987A (Timmermann & Larson 1992).  This observation raised the
possibility that oxygen-rich red supergiants might be a primary
cosmic source of hydrated silicate dust because SN 1987A's progenitor
was an ordinary red supergiant during its evolution before it
exploded.  This knowledge is important in a general astrophysical
context, and it has special relevance to understanding how the
composition of the ISM might have influenced thermochemical evolution
in our primordial solar nebula.  That is, it is not clear whether
hydrated silicates that have actually been observed in primitive
Solar System objects (e.g., asteroid surface minerals, carbonaceous
chondrite meteorites) originated in the ISM or were produced in the
solar nebula or the planetesimals themselves.  We therefore propose a
survey of O-rich red supergiants and other stellar sources where H2O
associated with mass loss episodes may have led to the formation of
hydrated silicates.