At just 10 centimetres deep, the pond does not freeze even as the surrounding landscape remains frozen.
The pond has a salinity of about 40%, making it one of the saltiest natural bodies of water on Earth.
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Calcium chloride accounts for up to 95% of its dissolved salts. The compound is highly soluble and binds strongly to water molecules, preventing them from forming the crystalline structure needed for ice. As a result, the pond’s freezing point is lowered so significantly that it remains liquid even in extreme sub-zero temperatures.
Comparison with the Dead Sea
The Dead Sea, often cited as one of the world’s saltiest lakes, has a salinity of 33-34%, lower than Don Juan Pond’s. By some estimates, Don Juan Pond is around 12 times saltier than seawater.
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Few other places approach this level of salinity, including Ethiopia’s Gaet’ale Pond and Senegal’s Lake Retba.
Source of the water remains unresolved
Scientists have yet to determine with certainty where the pond’s water and salt originate. The question has remained unanswered for more than 60 years.
One theory suggests that groundwater rises from beneath the surface, carrying dissolved minerals into the pond.Also Read: Extinct sand tiger shark teeth found in Antarctica reveal earth’s climate history
Another theory, proposed by geologists in 2013, suggests that salt-rich soils on nearby slopes absorb moisture from the atmosphere, which then flows downhill into the pond.
Neither theory has been confirmed, and the origin of the pond’s water and salts remains the subject of scientific debate.
Relevance to Mars research
The Dry Valleys’ combination of extreme cold, aridity and high salinity makes the region one of the closest Earth-based analogues to conditions on Mars.
Researchers say that if microbial life can survive in Don Juan Pond’s brine, similar organisms may once have existed, or could still exist, in comparable saline environments on Mars.
This possibility is the main reason the pond continues to attract scientific interest.