title: Perennial water ice identified in the south polar cap of Mars.
abstract: The inventory of water and carbon dioxide reservoirs on Mars are important clues for understanding the geological, climatic and potentially exobiological evolution of the planet. From the early mapping observation of the permanent ice caps on the martian poles, the northern cap was believed to be mainly composed of water ice, whereas the southern cap was thought to be constituted of carbon dioxide ice. However, recent missions (NASA missions Mars Global Surveyor and Odyssey) have revealed surface structures, altimetry profiles, underlying buried hydrogen, and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide. Here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes, at a resolution of 2 km, during the local summer, when the extent of the polar ice is at its minimum. We observe that this south polar cap contains perennial water ice in extended areas: as a small admixture to carbon dioxide in the bright regions; associated with dust, without carbon dioxide, at the edges of this bright cap; and, unexpectedly, in large areas tens of kilometres away from the bright cap.
authors.affiliation: Institut d'Astrophysique Spatiale, Orsay Campus, 91405, France. bibring@ias.u-psud.fr
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bibring
authors.forename: Yves
authors.initials: Y
authors.lastname: Langevin
authors.forename: François
authors.initials: F
authors.lastname: Poulet
authors.forename: Aline
authors.initials: A
authors.lastname: Gendrin
authors.forename: Brigitte
authors.initials: B
authors.lastname: Gondet
authors.forename: Michel
authors.initials: M
authors.lastname: Berthé
authors.forename: Alain
authors.initials: A
authors.lastname: Soufflot
authors.forename: Pierre
authors.initials: P
authors.lastname: Drossart
authors.forename: Michel
authors.initials: M
authors.lastname: Combes
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Bellucci
authors.forename: Vassili
authors.initials: V
authors.lastname: Moroz
authors.forename: Nicolas
authors.initials: N
authors.lastname: Mangold
authors.forename: Bernard
authors.initials: B
authors.lastname: Schmitt
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis / Q000737:chemistry; D018559:Exobiology; D005118:Extraterrestrial Environment / Q000737:chemistry*; D005843:Geography; D007053:Ice / Q000032:analysis*; D018535:Mars; D014867:Water / Q000032:analysis* / Q000737:chemistry
chemical_list: D007053:Ice; D014867:Water; D002245:Carbon Dioxide