A hypothetical picture of Mars 3.6 billion years ago, when an ocean may have covered nearly half the planet. The blue areas show the depth of the ocean filled to the shoreline level of the ancient, now-gone sea, dubbed Deuteronilus. The orange star represents the landing site of the Chinese rover Zhurong. The yellow star is the site of NASA’s Perseverance rover, which landed a few months before Zhurong.
(Credit: Robert Citron University of California – Berkeley)
A Chinese rover that landed on Mars in 2021 has detected underground beach deposits in a region believed to have once hosted an ancient sea, adding further evidence that the planet may have harbored a vast ocean billions of years ago.
The now-inactive Zhurong rover operated for a year, from May 2021 to May 2022, traveling 1.9 kilometers (1.2 miles) across an area suspected to be an ancient shoreline. Using ground-penetrating radar (GPR), it scanned up to 80 meters (260 feet) beneath the surface, revealing geological features consistent with beach deposits. The discovery strengthens the hypothesis that Mars had a thicker atmosphere and a warmer climate around 4 billion years ago, potentially supporting liquid water on its surface.
The radar was also able to determine the size of the particles in these layers, which matched that of sand. Yet, the deposits don’t resemble ancient, wind-blown dunes, which are common on Mars.
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“The structures don’t look like sand dunes. They don’t look like an impact crater. They don’t look like lava flows. That’s when we started thinking about oceans,” said Michael Manga, a University of California, Berkeley, professor of earth and planetary science. “The orientation of these features are parallel to what the old shoreline would have been. They have both the right orientation and the right slope to support the idea that there was an ocean for a long period of time to accumulate the sand-like beach.”
Manga is the contributing author of a paper about the Zhurong measurements to be published the week of Feb. 24 in the journal Proceedings of the National Academy of Sciences.
According to the paper’s Chinese and American authors, beaches imply a large, ice-free ocean on Mars, even though Mars is too cold today for water to flow as a liquid. They also imply that there were rivers that dumped sediment into the ocean that was distributed by waves along the beaches.
“The presence of these deposits requires that a good swath of the planet, at least, was hydrologically active for a prolonged period in order to provide this growing shoreline with water, sediment and potentially nutrients,” said co-author Benjamin Cardenas, an assistant professor of geosciences at The Pennsylvania State University (Penn State).
“This strengthens the case for past habitability in this region on Mars,” said Hai Liu, a professor with the School of Civil Engineering and Transportation at Guangzhou University and a core member of the science team for the Tianwen-1 mission, which included China’s first Mars rover, Zhurong.
In January 2025, other researchers reported evidence of ripples in sedimentary rocks at the bottom of Gale Crater, the landing site for NASA’s Curiosity rover, suggesting the presence of long-gone bodies of liquid water with no ice covering the surface. The Perseverance rover has also found evidence of a river delta in Jezero crater, a mere 2,400 kilometers (1,500 miles) from Zhurong’s landing site. But both of these craters are thought to have been lakes, not oceans.
“To make ripples by waves, you need to have an ice-free lake. Now we’re saying we have an ice-free ocean. And rather than ripples, we’re seeing beaches,” Manga said.
