Mars may once have had an ocean with sandy beaches, radar data suggests

The Guardian

24-02-2025

Mars may once have been home to sandy beaches, new ground-penetrating radar data suggests.
The radar data from China's Zhurong rover has revealed buried beneath the Martian surface evidence of what look like sandy beaches from the shoreline of a large ocean that may have existed long ago on the planet's northern plains.
The findings are the latest evidence indicating the existence of this hypothesised ocean, called Deuteronilus, roughly 3.5 to 4bn years ago, a time when Mars – now cold and desolate – had a thicker atmosphere and warmer climate. Scientists say an ocean of liquid water on the Martian surface could have harboured living organisms, much like the primordial seas of early Earth.
The rover, which operated from May 2021 to May 2022, travelled 1.2 miles (1.9 km) in an area that exhibits surface features suggestive of an ancient shoreline. Its ground-penetrating radar, which transmitted high-frequency radio waves into the ground that reflected off subsurface features, probed up to 80 metres beneath the surface.
Between 10 and 35 metres underground, the radar images detected thick layers of material with properties similar to sand, all sloped in the same direction and at an angle similar to that of beaches on Earth just below the water where the sea meets the land. The researchers mapped these structures spanning three-quarters of a mile along the rover's path.
'The Martian surface has changed dramatically over 3.5bn years, but by using ground-penetrating radar we found direct evidence of coastal deposits that weren't visible from the surface,' said Hai Liu, a Guangzhou University planetary scientist and a member of the science team for China's Tianwen-1 mission that included the rover.
On Earth, beach deposits of this size would have needed millions of years to form, the researchers said, suggesting that on Mars there was a large and long-lived body of water with wave action that distributed sediments carried into it by rivers flowing from nearby highlands.
'The beaches would have been formed by similar processes to those on Earth – waves and tides,' said Liu, one of the leaders of the study published on Monday in the journal Proceedings of the National Academy of Sciences. 'Such oceans would have profoundly influenced Mars' climate, shaped its landscape and created environments potentially suitable for life to emerge and thrive.'
'Shorelines are great locations to look for evidence of past life,' said Michael Manga, a planetary scientist and study co-author from the University of California, Berkeley. 'It's thought that the earliest life on Earth began at locations like this, near the interface of air and shallow water.'
The rover explored the southern part of Utopia Planitia, a large plain in the Martian northern hemisphere.
The researchers ruled out other possible explanations for the structures Zhurong detected.
'A primary part of this work was testing these other hypotheses. Wind-blown dunes were considered, but there were a few issues. First, dunes tend to come in groups, and these groups produce characteristic patterns not present in these deposits,' said Benjamin Cardenas, a Penn State geoscientist and study co-author. 'We also considered ancient rivers, which exist in some nearby locations on Mars, but we rejected that hypothesis for similar reasons based on the patterns we saw in the deposits. And you don't typically get structures like this in lava flows, either. Beaches simply fit the observations the best.'
Earth, Mars and the solar system's other planets were formed roughly 4.5bn years ago. That means Deuteronilus would have disappeared approximately 1bn years into Martian history, when the planet's climate changed dramatically. Scientists said some of the water may have been lost to space while large amounts may remain trapped underground.
A study published last year based on seismic data obtained by Nasa's robotic InSight lander found that an immense reservoir of liquid water may reside deep under the Martian surface within fractured igneous rocks.
For decades, scientists have used satellite images to trace Martian surface features resembling a shoreline. But any such evidence on the surface could have been erased or distorted by billions of years of wind erosion or other geological processes.
That is not the case with the newly found structures, which were entombed over time under material deposited by dust storms, meteorite strikes or volcanism.
'These are beautifully preserved because they are still buried in the Martian subsurface,' Cardenas said.