=====================================================================
==> In this proposal, more time is being requested for CONTRAST.LCOLANGE
=====================================================================
The goal of this proposal is to extend the study started with the ISO
program  CONTRAST,  aimed  at  analysing  dynamical  and  composition
properties of grains emitted from comet nuclei and present  in  their
trails. Comets, the best reservoir of pristine  cosmic  dust  in  the
solar system, have been the subject  of  past  space  missions  (e.g.
Giotto) and will be  the  target  of  the next ESA ambitious  Rosetta
project. The ISO facility is a powerful tool for imaging analysis  of
faint cometary dust trails and comae,  not  detectable  by  means  of
ground-based observations. Moreover, the ISO data represent a key  to
better interpret ground-based observations in the visible range,  for
the target comets. In our previous ISO program  CONTRAST  we  planned
coma and trail observations  of  46P/Wirtanen  (Nov.'96),  the  prime
target of the  Rosetta  mission,  and  of  65P/Gunn  (Mar.'96),  both
members of the Jupiter family,  to  gain  information  on  dynamical,
morphological and chemical properties of solid particles  distributed
in the coma and trail. ISO data, combined with  visible  ground-based
observations and used as input of models, allow us to determine grain
characteristics. On this ground, the  present  project  is  aimed  at
extending our approach to a larger set of comets,  mainly  pertaining
to the Jupiter family. Such a systematic analysis will  allow  us  to
identify  variation  ranges  and  possible  similarities  in  typical
physical parameters of such objects. The scientific follow-up has  to
be considered also in the perspective of  the  Rosetta  mission.  The
results of the present project will improve our knowledge of cometary
bodies and,  more  specifically,  will  help  to  better  define  the
objectives and operational plan of the Rosetta mission.