Gypsum crystals on Mars hint at standing water far more recently than models allow

For decades the standard picture has held that the surface of Mars froze solid roughly three billion years ago and never thawed again. A new analysis of data from China’s Zhurong rover challenges that timeline directly. Researchers led by Jiacheng Liu at the University of Hong Kong report mineral crystals in Utopia Planitia that, by their interpretation, could only have grown in standing liquid water — on a patch of Martian ground far younger than the frozen-surface model predicts. The work was published in Nature Astronomy.

A mission cut short, its data still yielding

Zhurong landed in Utopia Planitia, a vast plain in the Martian northern hemisphere, in May 2021. It spent 93 days gathering surface data before a dust storm ended its mission in 2022. During that window, its cameras photographed bright, flat rocks poking through the sand, and its instruments returned readings hinting the rocks were rich in water-bearing minerals — but the images alone were not enough to pin down exactly what those minerals were.

Liu’s team went back to that leftover data and looked more closely, this time at the shapes of tiny crystals visible just beneath the rocks’ surfaces. Some curled like cabbage leaves; others branched like Christmas trees. Combining measurements from the rover’s laser and infrared spectroscopy instruments, the team identified the crystals as selenite — a large-crystal form of gypsum that grows only by crystallizing directly out of concentrated salty water.

Reading the water from the rock

The presence of selenite is the crux, because it does not form any other way. From the thickness of the mineral layer, the team calculated that producing it would have required the equivalent of a water layer between about 6.25 and 25 meters deep, pooling at the surface over time. This was standing water, not a fleeting trace.

The bigger surprise is the age. Judging by the density of surrounding impact craters, the team estimated the ground itself at roughly 757 million years old — hundreds of millions of years more recent than most models allow for any surface water on Mars. Their proposed explanation ties it to the planet’s interior: underground brine, melted and driven upward by heat from volcanic activity, then trapped and concentrated at the surface as it froze from the top down.

A sealed snapshot for future missions

If the measurements hold, they push the possible persistence of Martian surface water far later into the planet’s history than the conventional timeline permits. And selenite carries a bonus: as it crystallizes, it can seal tiny pockets of the very liquid it formed from, potentially preserving a chemical snapshot of that ancient salty environment.

That makes this stretch of Utopia Planitia a compelling target for a future rover equipped to probe the environments locked inside crystal structures — a place where the record of relatively recent Martian water may still be sealed in the rock, waiting to be read.

© 2026 Homer Dávila Gutiérrez, FRAS — SKYCR.ORG. All rights reserved. Publication: 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