A new study suggests that Mars once had an ocean around 3.6 billion years ago.

Callisto, Io, Ganymede, Europa… these are just a few of the celestial bodies scientists believe could harbor life. Mars, as it turns out, may have had sunny beaches with gentle waves, perfect for a “vacation.” This conclusion comes from a team of international scientists who analyzed layers of rock beneath the Martian surface, providing evidence that Mars once hosted a massive northern ocean.

The study is based on data collected by Zhurong, the Chinese rover that traveled 1.9 kilometers through Utopia Planitia from May 2021 to May 2022, an area believed to have once been a sunbathed coastline of an ocean around 4 billion years ago when Mars had a thicker atmosphere and a warmer climate.

To reach these findings, the international team of scientists identified hidden rock layers beneath the planet’s surface, strongly suggesting the presence of a northern ocean. This new research offers the clearest evidence yet that Mars once contained a substantial body of water and a potentially habitable environment for life, according to Benjamin Cardenas, assistant professor of geology at Penn State and co-author of the study. “We’re finding places on Mars that look like ancient beaches and old river deltas,” Cardenas highlights. “We found evidence of wind, waves, and lots of sand: a perfect beach for a vacation.”

The Zhurong rover landed on Mars in 2021 in an area known as Utopia Planitia and sent back data about the geology of its surroundings in search of ancient signs of water or ice. Unlike other rovers, it was equipped with a penetrating radar, allowing it to explore the Martian subsurface. The rover used both low and high-frequency radar to penetrate the Martian soil and identify buried rock formations.

By studying underground sediment deposits, scientists can piece together a more complete picture of the planet’s history, explains Cardenas. When the team reviewed the radar data, they discovered a layered structure similar to Earth’s beaches: formations called “coastal deposits” that slope down toward oceans and form when sediments are transported by tides and waves into a large body of water.

“We immediately noticed this because it suggests that there were waves, which means there was a dynamic interface between air and water,” Cardenas insists. “When we look back and see where early life developed on Earth, it was in the interaction between oceans and land, so this shows us a picture of ancient habitable environments capable of hosting conditions favorable for microbial life.”

When the team compared the Martian data to radar images of coastal deposits on Earth, they found surprising similarities, according to Cardenas. The angles of the slopes observed on Mars were within the range found in coastal sedimentary deposits on Earth. The researchers also ruled out other possible origins for the inclined reflectors, such as ancient river flows, wind, or volcanic activity. They suggested that the consistent sloped shape of the formations, as well as the thickness of the sediments, point to a coastal origin.

“We’re seeing that the shoreline of this body of water evolved,” Cardenas notes. “We tend to think of Mars as a simple static snapshot of a planet, but it was evolving. Rivers were flowing, sediments were moving, and land was being formed and eroded. This type of sedimentary geology can tell us what the landscape was like, how it evolved, and most importantly, help us identify where we might look for past life.”

The discovery indicates that Mars was much wetter in the past than it is today, further supporting the hypothesis that there was once an ocean covering much of the planet’s northern pole. The study also provides new insights into the evolution of Mars’ environment, suggesting that a warm and wet period favorable for life may have lasted for tens of millions of years.

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