Observations in the Saturn system during approach and orbital insertion, with Cassini's visual and infrared mapping spectrometer (VIMS)

¹ Department of Planetary Sciences, and Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Boulevard, Tucson, AZ 85721, USA e-mail: rhb@lpl.arizona.edu
² Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Boulevard, Pasadena, CA 91109, USA
³ Consiglio Nazionale delle Ricerche, Isituto di Fisica dello Spazio Interplanetario, Via Fosso del Cavaliere, Tor Vergata, 00133 Roma, Italy
⁴ Consiglio Nazionale delle Ricerche, Isituto di Astrofisica Spaziale, via Fosso del Cavaliere, Tor Vergata, 00133 Roma, Italy
⁵ Mail Stop 964, US Geological Survey, Box 25046, Denver Federal Center, Denver, CO 80225, USA
⁶ Mail Stop 245-6, NASA Ames Research Center, Moffett Field, California 94035, USA
⁷ Observatoire de Paris, Meudon, Department de Recherche Spatial, 5 Place Jules Janssen, 92195 Meudon Cedex, France
⁸ Institute for Planetary Exploration, Deutsches Zentrum for Luft und Raumfahrt, Rudower Chausee 5, 12489 Berlin, Germany
⁹ Institute d'Astrophysique Spatiale, Université de Paris, Bâtiment 121, 91405 Orsay Cedex, France
¹⁰ Department of Earth and Space Sciences, Johnson Annex A, Box 351310, University of Washington, Seattle WA 98195, USA
¹¹ Istituto Nazionale di Astrofisica, Observatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
¹² Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
¹³ Laboratoire de Planetologie et Geodynamique, UMR - CNRS 6112, Faculty des Sciences, BP 92208, 2 rue de la Houssenire, 44072 Nantes Cedex 03, France

Received: 13 March 2005
Accepted: 8 August 2005

Abstract

The Visual and Infrared Mapping Spectrometer observed Phoebe, Iapetus, Titan and Saturn's rings during Cassini's approach and orbital insertion. Phoebe's surface contains water ice, CO₂, and ferrous iron. Iapetus contains CO₂ and organic materials. Titan's atmosphere shows methane fluorescence, and night-side atmospheric emission that may be CO₂ and CH₃D. As determined from cloud motions, the winds at altitude 25–30 km in the south polar region of Titan appear to be moving in a prograde direction at velocity ∼1 m s^-1. Circular albedo features on Titan's surface, seen at 2.02 μm, may be palimpsests remaining from the rheological adjustment of ancient impact craters. As such, their long-term persistence is of special interest in view of the expected precipitation of liquids and solids from the atmosphere. Saturn's rings have changed little in their radial structure since the Voyager flybys in the early 1980s. Spectral absorption bands tentatively attributed to Fe²⁺ suggest that iron-bearing silicates are a source of contamination of the C ring and the Cassini Division.