Using data gathered by China’s Zhurong rover, planetary researchers have identified hidden layers of rock under the Martian surface that strongly suggest the presence of an ancient northern ocean.
A panoramic photo taken by China’s Zhurong rover on Mars. Image credit: National Astronomical Observatories.
“We’re finding places on Mars that used to look like ancient beaches and ancient river deltas,” said Penn State researcher Benjamin Cardenas, co-author of the study.
“We found evidence for wind, waves, no shortage of sand — a proper, vacation-style beach.”
The now-inactive Zhurong rover landed on Mars in 2021 in an area known as Utopia Planitia, and operated for a year, between May 2021 and May 2022.
It traveled 1.9 km (1.2 miles) roughly perpendicular to escarpments thought to be an ancient shoreline from a time — 4 billion years ago — when Mars had a thicker atmosphere and a warmer climate.
Along its path, the rover used ground penetrating radar to probe up to 80 m (260 feet) beneath the surface.
This radar is used to detect underground objects, such as pipes and utilities, but also irregular features.
The radar images showed thick layers of material along the entire path, all pointing upward toward the putative shoreline at about a 15-degree angle, nearly identical to the angle of beach deposits on Earth.
Deposits of this thickness on Earth would have taken millions of years to form, suggesting that Mars had a long-lived body of water with wave action to distribute the sediments along a sloping shoreline.
The radar was also able to determine the size of the particles in these layers, which matched that of sand.
Yet, the deposits don’t resemble ancient, wind-blown dunes, which are common on Mars.
“This stood out to us immediately because it suggests there were waves, which means there was a dynamic interface of air and water,” Dr. Cardenas said.
“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.”
“When we compared the Martian data with radar images of coastal deposits on Earth, we found striking similarities.”
“The dip angles observed on Mars fell right within the range of those seen in coastal sedimentary deposits on Earth.”
“We’re seeing that the shoreline of this body of water evolved over time,” Dr. Cardenas said.
“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 discovery indicates that Mars was once a much wetter place than it is today, further supporting the hypothesis of a past ocean that covered a large portion of the northern pole of the planet.”
The study also provides new information on the evolution of the Martian environment, suggesting that a life-friendly warm and wet period spanned potentially tens of millions of years.
“The capabilities of the Zhurong rover have allowed us to understand the geologic history of the planet in an entirely new way,” said University of California, Berkeley’s Professor Michael Manga.
“Its ground-penetrating radar gives us a view of the subsurface of the planet, which allows us to do geology that we could have never done before.”
“All these incredible advancements in technology have made it possible to do basic science that is revealing a trove of new information about Mars.”
The results were published in the Proceedings of the National Academy of Sciences.
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Jianhui Li et al. 2025. Ancient ocean coastal deposits imaged on Mars. PNAS 122 (9): e2422213122; doi: 10.1073/pnas.2422213122
