Yungay Atacama, Chile, and University Valley, Antarctica, as Mars analogs, based on aridity as indicated by soil salt profiles and other characteristics

The Atacama desert in Chile and the McMurdo Dry Valleys (MDV) in Antarctica are considered to be two of the most arid deserts on Earth and thus are often used as Mars analogs for a variety of studies and instrument testing. Two regions within each of these, the Yunguy (Atacama) and University Valley (MDV) have especially been the focus of recent analog investigations. Both regions are comprised of soils that have accumulated an influx of atmospheric and marine salts. Some of these salts are influenced by the local biogeochemical environment and often display lower solubility. Two anions however, nitrate and perchlorate, are highly soluble species that represent proxies for the movement of water through the soil column either in bulk or thin films. An examination of these salt profiles in the upper and lower MDVs, and Yunguy, in the first case a relatively continuous and smooth distribution, while in the latter cases more chaotic and heterogeneous, suggests that University Valley has been subjected to little if any aqueous activity compared to Yungay or lower elevation MDVs. Even though Atacama possess some desirable Mars analog properties, the salt-profile-based aridity, the presence of dry permafrost, diffusion-controlled ice-table, cryoturbation, and comparatively pristine environment, endows the high elevation MDVs with unique and most Mars-like properties of any terrestrial analog site available.