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The role of remote sensing in the Rosetta mission

Cometary nuclei are considered the most important reservoir of primordial material from which the solar system formed about 4.6/spl times/10/sup 9/ years ago. Moreover, they should represent an uncontaminated "laboratory" where physical and chemical processes, active during the early stages of the solar system evolution, left their sign. Thus, the exploration of comets is a fundamental "milestone" for the understanding of cosmic physics phenomena concerning our planetary system and-more in general-active in the interstellar medium. The success of space missions was tested when comet P/Halley was visited in 1986. The Rosetta mission will follow a comet for a long period of time, up to the perihelion. Remote and in situ measurements will allow observation of a quiet nucleus, to detect the onset of activity and to monitor the emission evolution volatiles and grains. The properties of active and inactive surface regions will be studied and a complete mapping of the nucleus will be performed. Dynamics and chemicophysical processes active in the coma will be analysed. Science packages will be delivered to the cometary surface for "on-comet" measurements.