1. Planetary Science Institute; 1700 E. Ft. Lowell Tucson Arizona 85719 USA
2. Lancaster Environment Centre; Lancaster University; Lancaster LA1 4YQ UK
3. Observatoire de la Côte d'Azur; UMR 6202 Cassiopée; CNRS; BP 4229 06304 Nice Cedex 4 France
4. Physics Institute; Space Research and Planetary Sciences; Center for Space and Habitability; University of Bern; Bern Switzerland