China’s Zhurong rover has uncovered compelling evidence that Mars may have once been home to a vast ocean, complete with sandy beaches similar to those on Earth. The findings, based on ground-penetrating radar data collected during the rover’s 2021–2022 mission, provide some of the strongest support yet for the existence of an ancient Martian ocean called Deuteronilus, which may have covered parts of the planet’s northern plains around 3.5 to 4 billion years ago.
Buried Beaches Beneath the Martian Surface
The Zhurong rover, which landed in Utopia Planitia, a large impact basin in Mars’ northern hemisphere, used its ground-penetrating radar to examine up to 80 meters (260 feet) below the surface. The radar detected thick layers of material resembling sand, sloping in the same direction at an angle consistent with Earth’s beaches. These features were found 33 to 115 feet (10 to 35 meters) underground and spanned nearly 1.2 kilometers (three-quarters of a mile) along the rover’s path.
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According to Hai Liu, a planetary scientist from Guangzhou University and a member of China’s Tianwen-1 mission, the radar images offer “direct evidence of coastal deposits that weren’t visible from the surface.” Researchers believe these deposits formed when Mars had a thicker atmosphere and a warmer climate, allowing liquid water to exist on its surface.
Case for a Martian Ocean
Scientists have long debated whether Mars once had large bodies of water. Satellite images have hinted at shoreline-like features, but billions of years of erosion from wind, meteorite impacts, and volcanic activity may have obscured or erased surface evidence.
The new findings help resolve these uncertainties. Michael Manga, a planetary scientist at the University of California, Berkeley, emphasized the significance of these deposits, stating, “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.”
Formation of Mars’ Ancient Shores
On Earth, the formation of beach deposits like those detected by Zhurong requires millions of years. This suggests that Mars once had a long-lived and large body of water with waves and tides that shaped the shoreline.
Benjamin Cardenas, a geoscientist at Penn State and co-author of the study, explained that the beaches likely formed in a manner similar to those on Earth. “The presence of these deposits requires that a good swath of the planet was hydrologically active for a prolonged period,” he said. This means rivers from Mars’ highlands may have carried sediment into the ocean, creating a dynamic and evolving shoreline.
Could Mars Have Hosted Life?
The discovery adds weight to theories that Mars was once a potentially habitable planet. Scientists believe that early Earth’s oceans played a crucial role in the emergence of life, and Mars’ ancient seas might have done the same.
“Shorelines are great locations to look for evidence of past life,” Manga said. The presence of stable, standing water for an extended period suggests conditions that could have supported microbial life.
What Happened to Mars’ Water?
If Mars had an ocean billions of years ago, where did all the water go? Scientists theorize that some of it escaped into space as Mars lost its protective atmosphere, while large amounts may still be trapped underground in the form of ice or bound in minerals.
A study last year, based on seismic data from NASA’s InSight lander, indicated that an immense underground reservoir of liquid water may still exist deep within the Martian crust. This suggests that, while Mars may no longer have a surface ocean, significant amounts of water could remain hidden beneath its dusty exterior.
Resolving a Longstanding Mystery
Scientists have debated Mars’ ocean hypothesis since the 1970s, when NASA’s Viking spacecraft first captured images of what looked like ancient shorelines. However, one major problem was that these supposed shorelines weren’t level, with some parts dipping as much as 6 miles (10 kilometers).
In 2007, Manga and his colleagues proposed that Mars’ Tharsis volcanic region—home to the largest volcanoes in the solar system—could have shifted the planet’s rotation, deforming the shoreline over time. This idea was revisited in 2017, and the new data from Zhurong strengthens the case that an ocean once existed in Mars’ northern lowlands.
Preserved Beneath the Surface
One of the most exciting aspects of this discovery is that the beach deposits remain intact beneath layers of dust and debris. Unlike surface features that have been eroded over billions of years, these subsurface structures are well-preserved, allowing scientists to study them in their original form.
Cardenas highlighted the importance of these untouched layers, stating, “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.”
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While Zhurong is now inactive, its discoveries pave the way for future missions to explore Mars’ subsurface in greater detail. The ongoing Perseverance rover mission, along with planned future landers, could help answer lingering questions about the history of water on Mars and the possibility of ancient life. As Manga put it, “Oceans have a large effect on climate, they shape the surface of planets, and they are potentially habitable environments.” The discovery of Martian beaches adds yet another piece to the puzzle of the Red Planet’s mysterious past, bringing scientists one step closer to understanding whether Mars was ever home to life.