A paper published April 28 in Science Advances elaborated on the rover's discovery, noting that it found signs of liquid water at sand dunes located at low latitudes. These dunes pointed toward the planet's equator and away from its poles.
Since landing in Mars' northern hemisphere in May 2021, the Zhurong rover has traveled to four crescent-shaped dunes in the Utopia Planitia area to examine their surface composition. The dunes located close to each other are coated with thin, commonly fractured crusts and ridges. According to the researchers, these features were formed by melting little pockets of "modern water" sometime between 400,000 and 1.4 million years ago. (Related: Scientists discover new evidence of liquid water on Mars.)
Lead study author Qin Xiaoguang of the Chinese Academy of Sciences said of the find: "This is important for understanding the evolutionary history of the Martian climate, looking for a habitable environment, and providing key clues for the future search for life."
Qin and his colleagues utilized data acquired by the Zhurong rover's navigation and terrain camera, multi-spectral camera and Mars surface composition detector. This allowed them to analyze the surface features and material compositions of dunes in the rover's landing area. Their study revealed that the surface layer of the dune was rich in hydrated sulfates, hydrated silica, iron oxide minerals and probably chlorides.
"According to the measured meteorological data by Zhurong and other Mars rovers, we inferred that these dune surface characteristics were related to the involvement of liquid saline water formed by the subsequent melting of frost/snow falling on the salt-containing dune surfaces when cooling occurs," added Qin.
The researchers also suggested a sequence of events for how this liquid water formation happened.
Unlike Earth, the tilt of Mars shifts considerably on timescales ranging between hundreds and millions of years. At the current 25-degree tilt on Mars' rotational axis, ice is present in comparatively moderate quantities at the north and south poles. Nevertheless, research has shown that ice increases near the equator when Mars is tilted more, while the poles grow bigger at very low angles.
The authors of the new study theorized that low latitudes cool during the Red Planet's large obliquity, which leads to frost and snow that solidifies dunes and leaves traces of saline water.
This happens despite the very low pressure and water vapor content that made it difficult for liquid water to ecologically exist on Mars today, which is the the reason why experts thought water could only exist in solid or gaseous forms there.
Of course, past studies have already shown that Mars could have held enough water to cover its entire surface. But that was more than four billion years ago, when the Red Planet was warmer and wetter and possibly had a thicker atmosphere.
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