==> In this proposal, more time is being requested for EGRUEN.TOOCOMBR
Comets comprise the most primitive material in the solar system.
Observations of their composition are diagnostic of the environment in
the early stage where the planets and other solar system bodies were
formed. Long-period comets may comprise even more primitive
material than short-period comets. Several short- periodic comets
(P/Kopff, P/Schwassmann-Wachmann 1, and 2060 Chiron are among
the ISO guaranteed time targets (see further below). In contrary to them,
Comet C/1995 O1 (Hale-Bopp), discovered on July,22 1995, is a long-
period comet, (but not a "new" comet in the Oort's classification) and its
previous orbital period is estimated between 3400 and 4200 years. A
typical long-periodic comet (e.g. with high eccentricity) is still missing.
As a Target of Opportunity an "Anonymous" new comet offers several
unique possibilities both for infrared spectroscopy and photometry:
Comparison of the characteristics of the dust component in "new"
comets with those of short periodical comets. It is suggested, that the
surface of a new comet is less processed by solar radiation heating
during the perihelion passages and more pristine material will be ejected
into the dust coma. Since there are about new 15 comets discovered per
year, there is a good chance that a moderate bright long-period (or
"new" comet in the Oort's definition) will be observable during the life
time of ISO. Therefore an "Anonymous" comet should be a Target of
Opportunity, in the case such comet will be discovered early enough
before the end of the ISO mission (nominally January, 1st 1998). A
typical example is the new comet C/1996 Q1 (Tabur), discovered on
August,19th 1996. It should be noted, that this comet could be a
potential ToO comet, due to its visibility over the revolutions 434 till
479. The brightness of this comet may be comparable, or even larger, to
that of P/Kopff taking the geocentric distance (~1.7 AU) and the
heliocentric distance (1.6 up to 2.3 AU) into account.