Liquid water may still exist on Mars, but it's likely around for only short periods of time and in very small amounts. Researchers said today that the Curiosity rover has detected salts on Mars capable of significantly lowering the freezing point of water. This would allow water, which is typically frozen on Mars, to take up a liquid state even in spite of the planet's frigid temperatures. The researchers' analysis leads them to believe that liquid water may exist in Mars' soil at night before evaporating again during the day. The results are being published today in the the journal Nature Geoscience.

"We have discovered the substance calcium perchlorate in the soil and, under the right conditions, it absorbs water vapor from the atmosphere," Morten Bo Madsen, a University of Copenhagen researcher and co-author of the paper, says in a statement. "Our measurements from the Curiosity rover’s weather monitoring station show that these conditions exist at night and just after sunrise in the winter."

The process would begin with water vapor in the air each night. After it condenses on Mars' surface, the salts — in the form of calcium perchlorate — then saturate the water, lowering its freezing point. The water should then be able to turn into a liquid and be absorbed by the soil. The researchers found these conditions in the Gale Crater, but they believe that the same conditions likely exist across Mars.

Researchers have already determined that Mars once held large quantities of liquid water, but that was quite some time ago. Signs of liquid water existing on other planets today are always exciting because, on Earth, water is a requirement for life. But the researchers of this paper suggest that just because Mars may have water, it isn't necessarily hospitable. Most of Mars' soil, they point out, is way too cold for the survival of any known forms of life.

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