For decades, astronomers have assumed that the Martian surface froze solid around 3 billion years ago and has stayed that way ever since. If this were really the case, any liquid water would have long since either been locked away underground or lost to space.
Yet through a new analysis of mineral data gathered by Zhurong, China’s first Mars rover, researchers led by Jiacheng Liu at the University of Hong Kong have discovered evidence that doesn’t support this theory. If their interpretations are correct, they would indicate the presence of mineral crystals that could only have formed in standing water on a patch of Martian ground far younger than anyone expected.
Their research has been published in Nature Astronomy.
Mission cut short
In May 2021, Zhurong landed in Utopia Planitia, a vast plain in Mars’ northern hemisphere. For 93 days, it collected a wealth of data on the Martian surface before a dust storm cut its mission short in 2022.
During that time, Zhurong’s cameras photographed bright, flat rocks poking through the sand, and its instruments beamed back readings hinting that the rocks were rich in water-bearing minerals. Based on these images alone, however, researchers struggled to pin down the exact mineral compositions of these rocks.
Hints of aqueous activity
In their study, Liu’s team re-examined Zhurong’s leftover data in more detail. This time, they focused on the shapes of tiny crystals visible just beneath the rocks’ surface: some curling like cabbage leaves and others branching like Christmas trees. Through combined measurements from the rover’s laser and infrared spectroscopy instruments, they determined that these shapes were produced by selenite, a large-crystal form of gypsum that can only grow by crystallizing directly out of concentrated salty water.
Using the thickness of the mineral layer, the researchers calculated that producing it would have required the equivalent of a water layer somewhere between 6.25 and 25 meters (20.5 to 82 feet) deep, pooling at the surface over time.
Judging by the density of surrounding craters, they estimated the age of the ground itself at roughly 757 million years. The team suggests the water came from underground brine, melted and pushed upward by heat from volcanic activity, then trapped and concentrated as it froze from the top down.
Inspiring future missions
If the team’s measurements are accurate, they would suggest that surface water could have persisted on Mars hundreds of millions of years later than most models suggest. Since selenite crystals can seal tiny pockets of the liquid they formed in, they could potentially preserve a chemical snapshot of this ancient environment.
In turn, this patch of Utopia Planitia could become a strong candidate for closer inspection by future rovers—equipped to study the ancient environments locked away inside crystal structures.
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Publication details
Jiacheng Liu et al, Primary evaporite in southern Utopia Planitia on Mars from Zhurong rover observations, Nature Astronomy (2026). DOI: 10.1038/s41550-026-02917-3
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Mars could have carried liquid water more recently than we thought (2026, August 10)
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