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==> In this proposal, more time is being requested for PLAMY.COMETNU3
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Compared to short-period comets for which we submitted a similar program to
observe their nucleus, a new comet will have retain even more pristine
clues  of the processes which took place during the formation of the Solar
System. It is possible that a new bright comet will be observable during
the time of ISO observations. We propose to study the nucleus of such a new
comet by  measuring its thermal emission in the 8-15 micron spectral band
as a function of time over approximately 15 hours i.e., the longest period
of time during a single orbit. As demonstrated by ground-based observations
under favorable conditions of a few comets devoid of coma (e.g., comet
P/Arend-Rigaux), the thermal light curve allows to determine, under minimal
assumptions, the size and shape of the nucleus and to study its rotational
properties. Compared to our program concerning short-period comets, we
propose here an independent determination of the surface temperature by
using 4 narrow- band filters as made possible by the expected large flux of
the nucleus. We shall also observe, as a "by-product",  the thermal
emission from the innermost dust coma and shall study possible dust
structures and follow  their temporal evolution.