The following document lists the file abstract/PLAMY_COMETNU4.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
===================================================================== ==> In this proposal, more time is being requested for PLAMY.COMETNU1 ===================================================================== Because they are extremely difficult to observe, cometary nuclei are poorly known objects in spite of their pristine nature and of their potential as probes to the origin and evolution of the solar system. We propose to study the nuclei of 4 short-period comets, P/Encke, P/Tempel-Tuttle, P/Wild2 and P/Elst-Pizzaro which may be considered a transition object (active asteroid ?), by measuring their thermal emission in the 8-15 micron spectral band as a function of time over approximately 10 hours (expected mean value of their rotational periods). 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 sizes and shapes of the nuclei and to study their rotational properties. 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. Our top priority goes to 3 cometary nuclei for which we have a similar and complementary program with the Hubble Space Telescope: P/Encke and P/Tempel-Tuttle for which we submitted a proposal for the forthcoming cycle 7 and P/Wild2, the target of the STARDUST mission, for which we shall shorthly sollicit Discretionary Director Time. Although simultaneous observations are excluded because of very different constraints, combining the thermal (ISO) and the visible (HST) observations, after proper correction for different viewing geometries, will allow to obtain additional information and constraints on these nuclei. In particular, it will be possible to derive their albedo which will give us information on their degree of mantling and on the composition of the mantle. Extending our knowledge and understanding of cometary nuclei as made uniquely possible by ISO (and HST) is essential in the context of the space exploration of primitive bodies (ROSETTA and STARDUST missions).