Buried between some 10 metres below the surface of Mars lie what appear to be the remnants of sandy beaches, evidence for a large ocean that may have existed on the now-desolate planet billions of years ago, reports Reuters.
The discovery comes courtesy of a study using data from the Zhurong rover, China’s first to land on another planet and the first non-American rover to visit Mars, which operated from May 2021 to May 2022. The 240-kilogram rover traversed a distance of around 1.9 kilometres in the southern part of Utopia Planitia, a large plain in the Martian northern hemisphere located within the largest known impact crater in the solar system, the Utopia Basin. While surface features pointed toward the possibility of an ancient shoreline there, it took ground-penetrating radar to reveal the smooth, gently sloping layers of sand several metres thick that fell in a shallow 15-degree slope typical of beaches here on Earth.
Researchers are still poring over the data gathered by Zhurong, which wildly exceeded its intended lifespan of 90 sols (93 Earth days), remaining active for more than 347 sols (358 days) before going inactive due to an approaching sandstorm and falling temperatures.
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A primary part of the researchers’ work entailed ruling out other possible explanations for the sandy slopes. Wind-blown dunes, ancient rivers, even lava flows were considered but none matched the characteristics and patterns seen in the deposits recorded by Zhurong. “Beaches simply fit the observations the best,” Benjamin Cardenas, study co-author and geoscientist at Penn State, told Reuters.
Beach deposits of this size took millions of years to form on Earth, suggesting a large and long-lived body of water with waves that could distribute the sediments carried into it by rivers flowing from nearby highlands. It supports the hypothesised Deuteronilus, an ocean dating back roughly 3.5 to 4 billion years ago to when the planet had a thicker atmosphere, and the possibility of a life-friendly warm and wet period spanning potentially tens of millions of years.
“Shorelines are great locations to look for evidence of past life,” Michael Manga, study co-author and planetary scientist at the University of California, Berkeley, told Reuters. Life on Mars, if it existed, likely ended when the climate changed dramatically approximately a billion years after the planet’s formation. Some of the vast ocean may have been lost to space while large amounts remained underground, a hypothesis supported by a study published last year.
