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==> In this proposal, more time is being requested for DOSIP.PROP_COM
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The study of comets is of great importance to our understanding of the solar
system and its origin.  Comets comprise the most primitive material in the
solar system and observations of their composition are diagnostic of the
environment in which they formed. In recent taxonomic classification of
comets, we have clearly separated out the majority (~70%) of comets having
"typical" molecular abundances from a second distinct class of comets that
exhibit significant depletions in the carbon-chain species (C2 and C3).  The
ISO Guaranteed Time target, P/Kopff, as well as the Target of Opportunity
(ToO) comet Hale-Bopp are members of the "typical" class of comets.  Members
of the "carbon-chain depleted" class of comets must be studied in similar
detail as those of the "typical" class if we are indeed to gain a firm
understanding of the processes that took place during the early solar system.
Two of the three most extreme members of the the "carbon-chain depleted" class
are positioned favorably for observations by ISO. We are currently scheduled
for November 1996 observations of comet P/IRAS in order to complement the
existing Guaranteed time observations (DOSIP.PROP_COM).  Here, we propose to
extend the previously awarded time to also observe P/Wolf-Harrington which is
the most extreme member of the carbon-chain depleted class of comets and was
our primary Spring Launch target. This target has gas and dust production
levels approximately a factor of 3-5 below that of the principal GTO target,
P/Kopff and about 1% the production of P/Halley.  Results from this
observational programme are highly complementary to the Guaranteed Time
Observations of comets (EGRUEN.COMETS) as well as our current open time
observations (DOSIP.PROP_COM).