Antarctica’s Don Juan Pond stays liquid in one of the unlikeliest places on Earth, the frigid McMurdo Dry Valleys. The pond is the saltiest body of water on Earth, eight times brinier than the Dead Sea. The secret to how the pond stays moist and salty suggests the possibility of water flowing on the face of Mars.

A team lead by Brown University geologists discovered that Don Juan Pond gets its salt and some of its water from a nearby deposit of calcium chloride salt. The salt deposit sucks water from the icy air whenever the humidity increases. That salt laden water then slowly trickles downhill towards the pond. The rest of the pond’s water comes from occasional snow melt that helps to wash the salt into the pond.

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When the salt deposits suck moisture from the air they form dark streaks on the surface. Similar dark streaks, called slope lineae, have been documented on the down slope of cliffs on Mars.

Could these lines be a sign of tiny amounts of water flowing on Mars?

“Don Juan Pond is a closed basin pond and we just documented a couple hundred closed basins on Mars,” study co-author James Head of Brown said in a press release. “So what we found in Antarctica may be a key to how lakes worked on early Mars and also how moisture may flow on the surface today.”

“Broadly speaking, all the ingredients are there for a Don Juan Pond-type hydrology on Mars,” lead author James Dickson of Brown said in a press release. “It’s not likely that there’s enough water currently on Mars for the water to form ponds, but stronger flows in Mars’s past might have formed plenty of Don Juan Ponds.”

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Don Juan’s salty secret was documented using 16,000 images taken over a two month period. Changes in the pond’s appearance were correlated to environmental conditions, such as humidity. The study was published in Scientific Reports.

IMAGE: A camera installed above Don Juan Pond in Antarctica’s McMurdo Dry Valleys. (Geological Sciences/Brown University)