title: No signature of clear CO2 ice from the 'cryptic' regions in Mars' south seasonal polar cap.
abstract: The seasonal polar ice caps of Mars are composed mainly of CO2 ice. A region of low (< 30%) albedo has been observed within the south seasonal cap during early to mid-spring. The low temperature of this 'cryptic region' has been attributed to a clear slab of nearly pure CO2 ice, with the low albedo resulting from absorption by the underlying surface. Here we report near-infrared imaging spectroscopy of the south seasonal cap. The deep and broad CO2 absorption bands that are expected in the near-infrared with a thick transparent slab of CO2 ice are not observed. Models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a CO2 ice layer, which could be linked to atmospheric circulation patterns. The strength of the CO2 absorption increases after mid-spring, so part of the dust is either carried away or buried more deeply in the ice layer during the CO2 ice sublimation process.
authors.affiliation: Institut d'Astrophysique Spatiale, CNRS/Université Paris XI, Orsay Campus, 91405, France. yves.langevin@ias.u-psud.fr
authors.forename: Yves
authors.initials: Y
authors.lastname: Langevin
authors.forename: Sylvain
authors.initials: S
authors.lastname: Douté
authors.forename: Mathieu
authors.initials: M
authors.lastname: Vincendon
authors.forename: François
authors.initials: F
authors.lastname: Poulet
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bibring
authors.forename: Brigitte
authors.initials: B
authors.lastname: Gondet
authors.forename: Bernard
authors.initials: B
authors.lastname: Schmitt
authors.forename: F
authors.initials: F
authors.lastname: Forget