In 2021, a Chinese rover landed on Mars and detected evidence of underground beach deposits where the site of an ancient sea was once thought to be located. The rover, Zhurong, is now inactive, but it was in operation for a year between May 2021 and May 2022.
It traveled 1.2 miles along an ancient shoreline on Mars from four billion years ago, when the Red Planet had a warmer climate and a thicker atmosphere. The rover used ground-penetrating radar to probe up to 260 feet beneath the surface.
The radar images showed thick layers of material pointing upward at about a 15-degree angle. The discovery was very similar to the angle of beach deposits on Earth.
For deposits to become this thick on Earth, they would have taken millions of years to form, suggesting that Mars wasn’t always the dusty red desert we know today and was once home to an ancient body of water with waves.
The radar was also able to determine the size of the particles in the layers of material, which resembled sand. Yet, the deposits did not match the ancient, wind-blown dunes that are common on Mars.
“The structures don’t look like sand dunes. They don’t look like an impact crater. They don’t look like lava flows. That’s when we started thinking about oceans,” said Michael Manga, a professor of Earth and planetary sciences at the University of California, Berkeley.
“The orientation of these features are parallel to what the old shoreline would have been. They have both the right orientation and the right slope to support the idea that there was an ocean for a long period of time to accumulate the sand-like beach.”
If there were beaches on Mars, that means there was also a large, ice-free ocean, even though Mars is too cold today for water to exist in liquid form.
Additionally, it would imply that flowing rivers dumped sediments into the ocean that were then scattered by the waves along the shoreline.
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In the 1970s, the Viking spacecraft took images of Mars, which was what first led to the idea that an ocean once existed on the planet.
The images showed what appeared to be a shoreline around a large part of Mars’ northern hemisphere, as well as a depression that could represent a seabed.
However, the shoreline was so irregular that many scientists doubted the ancient ocean theory. Furthermore, the polar ice caps on Mars did not contain enough water to fill an ocean.
Later, missions to Mars found that a lot of the planet’s water may have escaped to space or gone underground as the planet cooled.
Last month, other researchers reported evidence of ripples in sedimentary rocks at the bottom of Gale Crater, where NASA’s Curiosity Rover landed, further supporting the idea that a liquid ocean with no ice on its surface existed.
“There has been a lot of shoreline work done, but it’s always a challenge to know how the last 3.5 billion years of erosion on Mars might have altered or completely erased evidence of an ocean. But not with these deposits. This is a very unique dataset,” said Benjamin Cardenas, a co-author of the study and an assistant professor of geosciences at Penn State.
The findings were published in Proceedings of the National Academy of Sciences.
