VIRTIS: an imaging spectrometer for the ROSETTA mission by Coradini, A, Capaccioni, F, Drossart, P, Semery, A, Arnold, G, Schade, U, Angrilli, F, Barucci, M, Bellucci, G, Bianchini, G, Bibring, J, Blanco, A, Blecka, M, Bockelee-Morvan, D, Bonsignori, R, Bouye, M, Bussoletti, E, Capria, M, Carlson, R, Carsenty, U, Cerroni, P, Colangeli, L, Combes, M, Combi, M, Crovisier, J