These are Antarctica's McMurdo Dry Valleys, so named because it literally never rains there... but this photo shows a patch of moisture. The salty soil is actually sucking water out of the atmosphere. And this discovery could be great news for Martian microbes.
Oregon State geologist Joseph Levy says the complete lack of precipitation doesn't stop the Dry Valleys from occasionally soaking up some moisture. The secret is just the right mix of salt in the soil, and enough humidity in the air. While the phenomenon has only been observed in Antarctica, it could potentially happen on any other desert on Earth, and even more excitingly it could theoretically occur on Mars and other alien worlds.
Here's how the process works, according to Levy:
"The soils in the area have a fair amount of salt from sea spray and from ancient fjords that flooded the region. Salts from snowflakes also settle into the valleys and can form areas of very salty soil. With the right kinds of salts, and enough humidity, those salty soils suck the water right out of the air. If you have sodium chloride, or table salt, you may need a day with 75 percent humidity to make it work. But if you have calcium chloride, even on a frigid day, you only need a humidity level above 35 percent to trigger the response. It's kind of like a siphon made from salt."
Levy and his colleagues found the moist soils had three to five times more water than elsewhere in McMurdo, and more importantly they were full of organic matter, including microbes. That last bit is exciting news for the prospect of microscopic life clinging to existence in the arid soils of Mars, particularly since previous studies of the Red Planet indicate it has sufficient humidity and the salty soils needed for this natural moisture-farming to work. As a bonus, the presence of all that salt in the soil would raise the freezing temperature of the water, helping the moisture to remain liquid. It's not proof by any means of Martian microbes, but this represents another very promising way for them to establish a foothold and thrive on an otherwise barren world.