In this study we assess the presence, nature and properties of ices - in
particular water ice - that occur within these spots using HIRISE and CRISM
observations, as well as the LMD Global Climate Model. Our studies focus on
Richardson crater (72{\deg}S, 179{\deg}E) and cover southern spring and summer
(LS 175{\deg} - 17 341{\deg}). Three units have been identified of these spots:
dark core, gray ring and bright halo. Each unit show characteristic changes as
the season progress. In winter, the whole area is covered by CO2 ice with H2O
ice contamination. Dark spots form during late winter and early spring. During
spring, the dark spots are located in a 10 cm thick depression compared to the
surrounding bright ice-rich layer. They are spectrally characterized by weak
CO2 ice signatures that probably result from spatial mixing of CO2 ice rich and
ice free regions within pixels, and from mixing of surface signatures due to
aerosols scattering. The bright halo shaped by winds shows stronger CO2
absorptions than the average ice covered terrain, which is consistent with a
formation process involving CO2 re-condensation. According to spectral,
morphological and modeling considerations, the gray ring is composed of a thin
layer of a few tens of {\mu}m of water ice. Two sources/processes could
participate to the enrichment of water ice in the gray ring unit: (i) water ice
condensation at the surface in early fall (prior to the condensation of a CO2
rich winter layer) or during winter time (due to cold trapping of the CO2
layer); (ii) ejection of dust grains surrounded by water ice by the geyser
activity responsible for the dark spot. In any case, water ice remains longer
in the gray ring unit after the complete sublimation of the CO2. Finally, we
also looked for liquid water in the near-IR CRISM spectra using linear unmixing
modeling but found no conclusive evidence for it
