The McMurdo Dry Valleys

The bare ground NASA uses as a stand-in for Mars

The McMurdo Dry Valleys are a series of largely snow-free desert valleys on the coast of Victoria Land, between the East Antarctic Ice Sheet and McMurdo Sound. At about 4,500 square kilometres they are the largest ice-free region in Antarctica, yet only around 0.03 percent of the continent, and they are the coldest and driest desert in the world. The Transantarctic Mountains, with peaks of some 3,000 metres, throw a snow shadow over them and hold back the glaciers. Katabatic winds, cold dense air pulled downhill by gravity, evaporate what snow does fall, in summer within hours, and a century of records averages about 100 mm of precipitation a year, almost all of it snow. The floors are loose gravel over granite and gneiss, broken into polygons by ice wedges.

For a few weeks each summer it is warm enough to melt glacial ice, and short streams run to lakes that have no outlet to the sea. There are more than 6,000 lakes and ponds; many keep a cap of ice all year, and with evaporation far exceeding precipitation, salts build up into saline and hypersaline water. The Onyx River, a meltwater stream, is the longest river in Antarctica. Temperatures have ranged from 12.0 °C at Taylor Glacier down to −65.7 °C at Lake Vida.

Life holds on in odd places. Endolithic bacteria live in the slightly moister interior of rocks, microbial mats line the melt streams, and anaerobic bacteria living on iron and sulfur survive beneath Taylor Glacier, where the red ice of Blood Falls is stained by iron oxide, not algae as was once thought. Higher up the limit is reached. In University Valley, about 1,700 metres up with a mean temperature of −23 °C and no days above freezing, the ice in the permafrost forms from water vapour rather than liquid water, and a 2013 expedition testing a drill designed for Mars found no living organisms in it, the first place visited by humans with no detected active microbial life.

The valleys were discovered in the early 1900s, and since NASA's Viking programme in the 1970s scientists have used them as a stand-in for the surface of Mars. Taylor Valley became a National Science Foundation Long Term Ecological Research site in 1992, and the area lies within the McMurdo Valleys Antarctic Specially Managed Area.