Mars was once home to a vast ocean, complete with sandy beaches and rolling waves, according to data from China’s Zhurong rover, which landed on the red planet in 2021.
New research published this week in the Proceedings of the National Academy of Sciences reveals underground rock layers that resemble coastal deposits on Earth, suggesting the presence of an ancient ocean billions of years ago on the red planet.
“We’re finding places on Mars that used to look like ancient beaches and ancient river deltas,” said Benjamin Cardenas, assistant professor of geology at Penn State and co-author of the study. “We found evidence for wind, waves, no shortage of sand — a proper, vacation-style beach.”
It supports the theory that Mars once had a much thicker atmosphere, allowing liquid water to exist on its surface for millions of years.
Radar Reveals Ancient Shoreline On Mars
Zhurong, part of China’s Tianwen-1 mission, landed in Utopia Planitia — a vast lava plain long suspected to have once been submerged under an ancient Martian ocean. Unlike previous rovers sent by NASA, Zhurong was equipped with ground-penetrating radar, enabling it to examine the planet’s subsurface.
As the rover traversed the red planet, it used radar to scan up to 260 feet (80 meters) beneath the surface. The scans revealed thick, sloping layers of material consistent with “foreshore deposits” seen in coastal regions on Earth. These formations form when waves and tides transport sediments along a shoreline.
“This stood out to us immediately because it suggests there were waves,” said Cardenas. “When we look back at where the earliest life on Earth developed, it was in the interaction between oceans and land, so this is painting a picture of ancient habitable environments, capable of harboring conditions friendly toward microbial life.”
A Long-Lived Ocean On Mars
The researchers ruled out other possible explanations, such as ancient river flows, wind-driven sand dunes and volcanic activity. “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.
All the evidence points to an old shoreline, supporting the idea that there was a large, ice-free ocean for a long period, which accumulated the sand-like beach. The researchers also think that there were rivers that dumped sediment into the ocean, which was distributed by waves along the beaches. “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,” said Manga.
It’s more evidence to support the theory that Mars had an ocean — and possibly rivers — in its northern hemisphere about four billion years ago, when the planet’s atmosphere was thick enough to sustain liquid water.
Implications For Climate And Life On Mars
Scientists have long debated how Mars lost its water. While some of it likely escaped into space, researchers believe much of it may still be trapped underground in ice or mineral formations.
Zhurong’s discovery also supports previous speculation that an ocean once covered Mars’s northern hemisphere — something suspected since the Viking missions to Mars in the 1970s. However, until now, direct evidence of a Martian shoreline has been elusive.
“Shoreline deposits are typically eroded over billions of years, but these have remained preserved beneath the surface,” said Cardenas. 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,” he said.
Future missions, including sample return efforts, may provide even more definitive proof of Mars’s watery past. For now, the idea of Martian beaches and waves offers an exciting glimpse into the planet’s ancient history — and its potential to have once supported life.
If you want to see Mars in the night sky from the Northern Hemisphere, just look high in the southeast after dark. It’s currently next to the two bright stars of Gemini, Castor and Pollux.
Wishing you clear skies and wide eyes.
