In this proposal, more time is being requested for our winning GO proposal for
the original ISO Call for Proposals, PERBRCO.CLISSE. As shown in our original
proposal, there is a critical need for thermal infrared mapping and photometric
observations of the extended dust tails of bright comets by orbiting cryogenic
infrared telescopes. Using time granted for our original proposal, we will
observe comet P/IRAS in October 1996. With this proposal for the supplemental
call, we will extend our scientific investigation to a second comet, chosen to
be the target of either the upcoming NASA STARDUST mission to collect cometary
dust, or the target of the upcoming ESA ROSETTA mission to rendezvous and land
on a comet. The results of our observations will be used to derive the amount
of dust emitted by the comet vs time and heliocentric distance, of vital
interest in maximizing the scientific return and minimizing the spacecraft
hazards during the flyby/rendezvous. We also propose to extend our investigation
to explore possible new cometary spectroscopic features, such as those related
to x-ray emission from comets and dust emission features found in proto-
planetary systems.
As for comet P/IRAS observed in October 1996, we will compare  the ISO imaging
and spectral data to simultaneous data obtained by the Lowell optical and NASA
/IRTF infrared ground based telescopes, as well as archival data obtained by
IRAS, COBE/DIRBE, HST, and  for relationships by cometary age, orbit, color
temperature, silicate feature, and trail formation. We will also request simul-
taneous ROSAT and ASCA observations, to look for correlations between infrared
and x-ray cometary emission.
The objects to be observed are any any of the following periodic comets listed
for Spring Launch in our first proposal (in order of preference): P/Wild2,
P/Wirtannen, P/Haneda-Campos, P/Wolf-Harrington, P/Taylor, P/Hartley 2, P/Temple
-Tuttle, P/Wild2, P/Gunn, any bright dynamically new comet with appropriate
orbital geometry.