MARTIAN SOUTH POLAR DEFORMATION AND SUBLIMATION

The first documented glacial deformations of an extraterrestrial ice sheet have been discovered at the Martian south polar cap in Mars Orbital Camera (MOC) images. Deformational features found are similar to those in terrestrial glaciers and include; boudinage, folds, and faults. The Martian environment is unique with the coexistence of dry ice (CO₂ ) and water ice and, hypothetically, CO₂ clathrate hydrate. The south polar cap is laterally heterogeneous in these ices (at least the first two) and vertically structured with a layered sequence of what may be interbedded ices. This type of glacier is not known on Earth. The stability of these ices is limited by temperature, pressure, and the availability of H₂O and CO₂ transported to the polar environment. As environmental conditions oscillate over the Martian year, a layered polar ice mass has been constructed. In addition, distinctive ice and dry-ice sublimation features exist. Sublimation erosion of the layered sequence of ices allows us to observe the internal structure of an active polar cap.

While both sublimation and deformation features appear in the South Polar cap of Mars, sublimation is much more apparent than deformation, when observing MOC images. Deformation features are not only rarer than sublimation features, but convincing examples are lacking. Boudins are especially troublesome on Mars as on Earth, as perfect boudins are a rarity. Polygons are widely distributed through out the study area and have been found at the surface as well as beneath other transparent layers. Spiders are found most abundantly on the residual part of the Polar cap. While other sublimation features are found predominantly on the perennial part of the cap. Layers are found anywhere there is dissected topography and are distributed in a majority of areas in this study. Swiss Cheese is most commonly found on the more permanent Ice cap. Most of the distribution differences can be attributed to differences in temperatures and radiation received or in ice type/abundance differences. The unequal nature in which the MOC images were initially collected by the Mars Global Surveyor (MGS) also contributes to the apparent concentrations of features.