Billions of Years Ago, Mars Featured Beaches Fit for a Vacation, Astronomers Say

Step aside, Santa Monica. It seems that Mars once had beaches that would give the Californian coast a run for its money.

An international team of researchers has revealed evidence of bygone “vacation-style” sandy beaches on Mars: underground rock layers that testify to an ancient northern ocean with gently lapping waves, as detailed in a study published January 14 in the journal PNAS. Their work bolsters previous research suggesting that Mars once hosted large bodies of water and a potentially habitable environment.

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

Cardenas and his colleagues studied geological data collected by the Chinese Zhurong rover in 2021 in an area of Mars called Utopia Planitia. Zhurong comes equipped with ground-penetrating radar, a tool that “gives us a view of the subsurface of the planet, which allows us to do geology that we could have never done before,” said Michael Manga, a planetary scientist at the University of California, Berkeley, who also participated in the study.

The radar data revealed underground rock layers bearing a striking resemblance to geological structures on Earth called “foreshore deposits”—downward sloping formations shaped by water currents pulling sediments into oceans. The researchers confirmed the similarities by comparing the Mars data to radar images of Earthly coastal deposits—even the angles of the underground Martian slopes aligned with those on our planet.

“This stood out to us immediately because it suggests there were waves, which means there was a dynamic interface of air and water,” Cardenas explained. “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.”

After making sure that the formation couldn’t be explained by other factors such as rivers, wind, or volcanic activity, the researchers suggest that the Martian formations, as well as the thickness of their sediments, imply the presence of a bygone oceanic coast.

“We’re seeing that the shoreline of this body of water evolved over time,” Cardenas added. “We tend to think about Mars as just a static snapshot of a planet, but it was evolving. Rivers were flowing, sediment was moving, and land was being built and eroded. This type of sedimentary geology can tell us what the landscape looked like, how they evolved, and, importantly, help us identify where we would want to look for past life.”

The study supports previous research claiming that Mars once had a giant ocean, while also suggesting that one of the Red Planet’s highly scrutinized warm and wet periods might have lasted tens of millions of years.

If Mars really had oceanfront property, its ancient shores might be some of the best places to hunt for signs of past life. Future missions could help settle the question: Did microbes once call these beaches home, or were they just waves rolling over an empty, lifeless world?