Brown, M. Langhans, J. Soderblom, L. A. Soderblom, S. Le Mouélic, R. N. Clark, B. J. Buratti, K. H. Baines, D. P. Cruikshank, P. D. Nicholson, G. Filacchione, R. Wagner, J. Barnes and R. M. Nelson DLR, Institute of Planetary Research. Rutherfordstrasse 2, 12489 Berlin, Germany; Dept. of Earth Sciences, Inst. of Geosciences, Freie Universität Berlin, Germany; Jet Propulsion Laboratory, California Institute of Technology, Pasadena CA 91109, USA; Lunar and Planetary Laboratory, University of Arizona, Tucson AZ 85721, USA; U.S. Geological Survey, Flagstaff, AZ 86011, USA; University of Nantes, 44072 Nantes Cedex 3, France; U.S. Geological Survey, Denver Federal Center, Denver CO 80225, USA; NASA Ames Research Center, 245-6, Moffett Field, CA 94035-1000, USA; Department of Astronomy, Cornell University, Ithaca, NY 14853, USA; Istituto Fisica Spazio Interplanetario, CNR, Via Fosso del Cavaliere, Roma, Italy; University of Idaho, Department of Physics, Moscow, ID 83844-0903; Corresponding author (Fax :+493067055 402 ; Email address: ralf.jaumann@dlr.de