VIRTIS: The imaging spectrometer of the ROSETTA mission

The study of minor bodies of the Solar System is acquiring an increasing importance in recent years thanks to new space missions, such as NEAR, and to new ground based observations. However none of the presently planned missions will be able to study targets, such as asteroids and comets with such a complete and state-of-the-art- payload, as will Rosetta mission. Rosetta will study in detail a comet nucleus, the prime target of the mission following it from large distances (more than 3 AU) inbound up to almost 1 AU from the Sun. This will permit the detection of the beginning of the cometary activity, as well as determining the composition of emitted gases. At the same time, modification of the cometary surface will be observed and analysed. Detailed in situ analysis will be performed by the Surface Science Package (SSP), thus allowing not only a detailed analysis of the selected landing site, but also establishing ground truth for the remote sensing experiment. VIRTIS (Visible Infra Red Thermal Imaging Spectrometer) is fundamental to the detection and study of the evolution of the typical spectral bands of minerals and molecules characterising the comet surface as well as those of gases and dust dispersed in the coma. Their identification is a primary goal of the Rosetta mission; this will allow the identification the nature of the main constituent of the comets. Moreover, the surface thermal evolution during comet approach to sun will be monitored. In this paper the VIRTIS design and its detailed science goals are reported. (C) 1999 COSPAR. Published by Elsevier Science Ltd.