Mars may have once had a vast, ice-free ocean, according to new evidence from China’s Zhurong rover.
Using ground-penetrating radar, the rover revealed sloping, sand-like deposits underground that strongly resemble beach formations on Earth. This discovery suggests that Mars had a long-lived, dynamic shoreline where waves distributed sediment — an environment that could have supported life.
Discovery of Ancient Beach Deposits on Mars
China’s Zhurong rover, which landed on Mars in 2021, has uncovered evidence of buried beach deposits in an area believed to have once been home to an ancient sea. This discovery adds to the growing evidence that Mars once had a vast ocean.
The rover, now inactive, operated for a year between May 2021 and May 2022. It traveled 1.9 kilometers (1.2 miles), moving roughly perpendicular to escarpments suspected to be the remnants of an ancient shoreline. This shoreline dates back about 4 billion years, a time when Mars had a thicker atmosphere and a warmer climate. Along its route, Zhurong used ground-penetrating radar (GPR) to scan up to 80 meters (260 feet) beneath the surface. This technology, commonly used on Earth to detect underground structures like pipes or rock boundaries, helped reveal what lay hidden beneath Mars’ terrain.
The radar images showed thick layers of material consistently sloping upward toward the suspected shoreline at an angle of about 15 degrees — closely matching the angle of beach deposits on Earth. On our planet, deposits of this thickness take millions of years to form, suggesting that Mars once had a stable, long-lived body of water where waves gradually built up sediment along a gently sloping shore.
A Strong Case for an Ancient Ocean
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.
“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 published in the journal Proceedings of the National Academy of Sciences.
Implications for Mars’ Climate and Habitability
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). “Shorelines are great locations to look for evidence of past life. It’s thought that the earliest life on Earth began at locations like this, near the interface of air and shallow water.”
“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.
The Enigma of the Deuteronilus Shoreline
Images taken by the Viking spacecraft in the 1970s first led to speculation that an ocean once existed on Mars, likely during a time when the planet had a denser atmosphere that could retain heat and thus liquid water. The Viking images showed what looked like a shoreline around a large portion of Mars’ northern hemisphere and a depression that could be an ancient seabed.
Yet, the shoreline was so irregular, with ups and downs of up to 10 km, that planetary scientists doubted this scenario. Shorelines, like those on Earth, should be level. Other conundrums, such as what happened to the water, also cast doubt on this theory. The polar ice caps do not contain enough water to fill such an ocean.
Could Mars Have Hidden Water Underground?
Subsequent missions to Mars, however, provided evidence that, while a lot of the planet’s water likely escaped to space along with Mars’ atmosphere as the planet cooled, much probably also went underground, either as ice or combined with rocks to form new minerals.
In 2007, Manga and his colleagues proposed a theory to explain how today’s uneven shoreline could have been created by an ocean. Based on computer modeling, they argued that the planet’s huge volcanic region, Tharsis, which contains the solar system’s largest volcanoes, altered the planet’s rotation after it formed about 3.7 billion years ago, making the level shoreline uneven. He revised that theory in 2017, suggesting that Mars’ rotation actually changed while the Tharsis bulge formed, starting about 4 billion years ago.
“Because the spin axis of Mars has changed, the shape of Mars has changed. And so what used to be flat is no longer flat,” he said.
With its ground penetrating radar, Zhurong had an opportunity to look for underground evidence of an ancient ocean.
Zhurong’s Unique Opportunity to Probe Below the Surface
“The southern Utopia Planitia, where Zhurong landed on May 15, 2021, is one of the largest impact basins on Mars and has long been hypothesized to have once contained an ancient ocean,” Liu said. “Studying this area provides a unique opportunity to investigate whether large bodies of water ever existed in Mars’ northern lowlands and to understand the planet’s climate history.”
Hai and Zhurong scientists reached out to Manga through Cardenas to help interpret the GPR data primarily because of Manga’s long interest in Mars’ oceans. Manga says that the Rover Penetrating Radar (RoPeR) detected radar reflections about 10 meters below the current surface that are classic indications of sloping, sandy beaches lining an ocean.
“The sand that’s on those beaches is coming in from the rivers, and then it’s being transported by currents in the ocean and continually being transported up and down the beaches by the waves coming and going up and down the beach,” Manga said, noting that Mars has many features that look like ancient rivers. “So there must have been rivers transporting sediment to the ocean, though there’s nothing in the immediate vicinity that would have disturbed these beach deposits.”
Other Evidence of Water on Mars Emerges
In February 2023, 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.
The approximately 10 meters (30 feet) of material overlaying the beach deposits were likely deposited by dust storms, material thrown out by asteroid impacts or volcanic eruptions over the billions of years since the ocean disappeared. This turned out to be fortuitous, Cardenas said.
Preserved in Time: An Untouched Martian Shoreline
“The shoreline deposits imaged here are pristine, still in the subsurface,” he said. “There has been a lot of shoreline work done, but it’s always a challenge to know how the last 3.5 billion years of erosion on Mars might have altered or completely erased evidence of an ocean. But not with these deposits. This is a very unique dataset.”
Explore Further: Stunning Rover Data Reveals Hidden Martian Shoreline
Reference: “Ancient ocean coastal deposits imaged on Mars” by Jianhui Li, Hai Liu, Xu Meng, Diwen Duan, Haijing Lu, Jinhai Zhang, Fengshou Zhang, Derek Elsworth, Benjamin T. Cardenas, Michael Manga, Bin Zhou and Guangyou Fang, 24 February 2025, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2422213122
Other co-authors of the paper are Liu’s colleagues at Guangzhou University, Jianhui Li, Xu Meng, Diwen Duan, and Haijing Lu; Jinhai Zhang, Bin Zhou, and Guangyou Fang of the Chinese Academy of Sciences in Beijing; Fengshou Zhang of Tongji University in Shanghai; and Derek Elsworth of Penn State. Fang, who is with the Aerospace Information Research Institute, developed the Rover Penetrating Radar for Tianwen-1.
The Chinese team was supported by the Natural Science Foundation of China and the Guangdong Basic and Applied Basic Research Foundation. Manga was supported by the Earth4D program of the Canadian Institute for Advanced Research.
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1 Comment
“It’s thought that the earliest life on Earth began at locations like this, near the interface of air and shallow water.”
Not by the faction who argue for undersea volcanic vents…