OMEGA Spectra of Different Regions in Mars's Southern Seasonal Cap
Reflectance spectra of representative regions within Mars's southern seasonal cap. The regions a-d are those identified in the OMEGA continuum image of the southern seasonal cap (see related images). Spectra are corrected for aerosol contributions and atmospheric absorption.
CO2 ice absorption bands are much deeper in region b (mean path length 10 cm) than in region a (mean path length 10 mm), hence region b is covered by much coarser CO2 ice than region a.
Strong water ice absorptions dominate the reflectance spectrum of region c. The weak CO2 absorption bands in spectra from the cryptic region (black curve, region d) cannot correspond to a surface covered by a slab of nearly pure CO2 ice, such as that observed by OMEGA in mid-winter (green spectrum, provided for reference).
Image reproduced from the publication by Y. Langevin et al "No signature of clear CO2 ice from the cryptic regions in Mars' south seasonal polar cap", Nature 442, 7104, pp 790-792, 2006