Mars, the dusty red planet we know today, may have once had ocean waves washing onto sandy beaches.
New research using data from China’s Zhurong rover has uncovered underground evidence of ancient beach deposits, offering some of the clearest signs yet that Mars had a vast, long-lasting ocean around four billion years ago.
The Zhurong rover, part of China’s Tianwen-1 mission, landed in a flat, low-lying region of Mars known as Utopia Planitia in May 2021.
Scientists have long suspected this area might once have been the floor of a massive ocean.
Over the course of a year, the rover traveled nearly two kilometers, moving toward what many believe to be a shoreline from Mars’ distant past.
During its journey, Zhurong used ground-penetrating radar to examine layers beneath the surface—up to 80 meters deep.
This type of radar, similar to what’s used on Earth to find buried pipes or ancient ruins, revealed tilted layers of sand-like material beneath the surface.
These layers pointed upward toward what would have been the shoreline and sloped at an angle of about 15 degrees, which is nearly identical to beach formations found on Earth.
These findings were recently published in the Proceedings of the National Academy of Sciences and include contributions from scientists in China and the United States.
Michael Manga, a geoscientist at the University of California, Berkeley, and a long-time expert on Martian oceans, helped interpret the radar data.
He explained that the structure and orientation of the buried layers looked nothing like sand dunes, lava flows, or impact craters. Instead, they matched beach deposits formed by waves in a large, ice-free ocean.
This isn’t the first time scientists have proposed the idea of an ocean on Mars. As far back as the 1970s, NASA’s Viking spacecraft captured images of what appeared to be a shoreline. However, that supposed shoreline wasn’t level, leading many to doubt whether it truly marked the edge of an ocean.
Later research, including computer models by Manga and others, suggested that changes in Mars’ rotation caused by massive volcanic activity could have tilted what was once a flat shoreline, explaining the uneven elevation.
The Zhurong rover’s data adds crucial new evidence. The buried beach deposits were preserved beneath about 10 meters of material—likely dust, volcanic ash, or debris from asteroid impacts—which protected them from erosion over billions of years.
That means these deposits remain “pristine,” according to Benjamin Cardenas of Penn State, another author of the study.
What’s especially exciting is what beaches represent: a dynamic environment where rivers deliver sediment and waves move it along the shore. These are also the kinds of places where life is believed to have first emerged on Earth. If Mars once had similar environments, it could have been a hospitable place for life, too.
The discovery gives scientists a stronger reason to keep exploring Utopia Planitia and other suspected ocean sites. It also opens up new opportunities to search for signs of past life, especially in shoreline areas where water, nutrients, and energy would have been abundant.
For now, the ancient beaches buried beneath Mars’ surface remain silent, but they tell a powerful story of a planet that may have once looked a lot like Earth.
