For decades, Mars has been a dusty, barren world in our imagination — a cold desert where water exists only as ice or vapor. But new evidence suggests the Red Planet was once home to something far more inviting: sun-soaked, sandy beaches.

This lost landscape was unveiled by Penn State, UC Berkeley, and Guangzhou University researchers, who pored over radar data from a Chinese rover named Zhurong that rolled across Mars in 2021. They spotted sloping rock formations (foreshore deposits) that mirror Earth’s beaches, tilting downward at angles that scream “oceanfront.”

“We’re finding places on Mars that used to look like ancient beaches and ancient river deltas,” says Benjamin Cardenas, a geologist at Penn State and co-author of the study. “We found evidence for wind, waves, no shortage of sand — a proper, vacation-style beach.”

A Window Beneath the Surface

Zhurong wielded ground-penetrating radar, a tool that let it peek beneath the Martian crust during its year-long trek, spanning 1.9 kilometers between May 2021 and May 2022. Using both low- and high-frequency waves, it mapped buried layers of sediment beneath its landing site in Utopia Planitia, a vast plain in Mars’ northern hemisphere.

What it found was remarkable: layers of sedimentary rock sloping downward at a 15-degree angle, a pattern eerily similar to the foreshore deposits found on Earth’s beaches. These formations are created when waves and tides carry sediment into a large body of water, leaving behind a telltale signature. These weren’t dunes or volcanic scars. They looked like beaches.

“This stood out to us immediately because it suggests there were waves, which means there was a dynamic interface of air and water,” Cardenas explains. That interface matters. On Earth, it’s where life likely first sparked—where wet sands met shallow seas. Could Mars have hosted something similar? The radar data says yes, painting a vivid picture of a once-habitable world.

“I was amazed however, just how uniform these layers are and how similar they look to beaches on Earth, even after three and a half billion years,” Michael Manga, a planetary scientist at UC Berkeley and the study’s corresponding author, told ZME Science.

The sediment deposits — which the rover probed 80 meters deep — were made along a route perpendicular to what scientists suspect was a shoreline from 4 billion years ago. Back then, Mars boasted a thicker atmosphere, a warmer climate, and — apparently — liquid water aplenty.

Beaches don’t form in a puddle. They hint at a massive body of water, fed by rivers, shaped by currents, and alive with motion. “The presence of these deposits requires that a good swath of the planet, at least, was hydrologically active for a prolonged period,” says Cardenas.

A Wetter, Warmer Ancient Mars

The discovery adds weight to a theory that has intrigued scientists since the 1970s, when NASA’s Viking spacecraft first captured images of what appeared to be a shoreline around Mars’ northern hemisphere. But the Viking images were puzzling. The shoreline was uneven, with elevations varying by up to 10 kilometers (6 miles) — far too irregular to match the flat shorelines seen on Earth. This inconsistency cast doubt on the idea of a Martian ocean.

Manga and his colleagues have spent years trying to solve this mystery. In 2007, they proposed that Mars’ rotation shifted billions of years ago, tilting the planet and warping its surface. This shift, driven by the growth of the massive Tharsis volcanic region, could explain why the shoreline appears uneven today. “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,” Manga explained.

This is far from the first hint of Mars’ watery past. NASA’s Curiosity rover found ripples in Gale Crater, signs of an ancient lake. Perseverance, trundling through Jezero Crater, is closely studying a fossilized river delta. Now, Zhurong’s discovery of an oceanic past ties these threads together. “The ripples record a past lake. The sloping beach deposits record a past ocean,” Manga explains. “Gale Crater is small and hence can host a lake. The northern lowlands of Mars can hold a large ocean.”

“This strengthens the case for past habitability in this region on Mars,” Manga added.

Together, these findings reshape Mars’ biography. Long ago, it wasn’t the barren wasteland we see today. Water coursed across its surface —lakes, rivers, and now an ocean that might have stretched across the northern pole. Cardenas sees a warm, wet era lasting tens of millions of years. “We’re seeing that the shoreline of this body of water evolved over time,” he says. “We tend to think about Mars as just a static snapshot of a planet, but it was evolving.”

What’s Next?

Zhurong’s mission ended in May 2022 after its solar panels were shaded by dust, but future missions could target these ancient shoreline deposits, drilling deeper to retrieve samples or using more advanced radar to map the subsurface in greater detail. “It would be lovely to send a new mission targeting these deposits where they might be excavated,” Manga said.

Meanwhile, NASA’s Perseverance rover at Jezero Crater is already collecting samples with the goal of returning them to Earth in the 2030s. While these samples won’t include material from the ancient ocean, they could provide insights into Mars’ wetter past.

For now, the discovery of ancient beaches on Mars offers a glimpse into a time when the Red Planet may have been a blue one, with waves lapping at its shores and rivers carving paths across its surface. It’s a reminder that Mars, now a barren desert, was once a world teeming with possibility. And maybe even life.

The findings appeared in the Proceedings of the National Academy of Sciences.