1. Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, 00133 Roma, Italy.
2. Agenzia Spaziale Italiana, Via del Politecnico, 00133 Roma, Italy.
3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
4. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
5. Southwest Research Institute, 1050 Walnut Street, Boulder, CO 80302, USA.
6. Earth Planetary and Space Sciences, University of California, Los Angeles, CA 90095, USA.