An international team of scientists, including Penn State researchers, used data from the Zhurong Mars rover to identify hidden layers of rock under the planet's surface that strongly suggest the presence of an ancient northern ocean. The new research offers the clearest evidence yet that the planet once contained a significant body of water and a more habitable environment for life, according to Benjamin Cardenas, assistant professor of geology at Penn State and co-author on the study.
"We're finding places on Mars that used to look like ancient beaches and ancient river deltas," Cardenas said. "We found evidence for wind, waves, no shortage of sand - a proper, vacation-style beach."
The Zhurong rover landed on Mars in 2021 in an area known as Utopia Planitia and sent back data on the geology of its surroundings in search of signs of ancient water or ice. Unlike other rovers, it came equipped with rover-penetrating radar, which allowed it to explore the planet's subsurface, using both low and high-frequency radar to penetrate the Martian soil and identify buried rock formations.
By studying the underground sedimentary deposits, scientists are able to piece together a more complete picture of the red planet's history, Cardenas explained. When the team reviewed radar data, it revealed a similar layered structure to beaches on Earth: formations called "foreshore deposits" that slope downwards towards oceans and form when sediments are carried by tides and waves into a large body of water.
"This stood out to us immediately because it suggests there were waves, which means there was a dynamic interface of air and water," 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 the team compared the Martian data with radar images of coastal deposits on Earth, they found striking similarities, Cardenas said. The dip angles observed on Mars fell right within the range of those seen in coastal sedimentary deposits on Earth.
The researchers also ruled out other possible origins for the dipping reflectors, such as ancient river flows, wind or ancient volcanic activity. They suggested that the consistent dipping 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 over time," 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, Cardenas explained. The study also provided 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 Michael Manga, professor of Earth and planetary science at the University of California, Berkeley, and a corresponding author on the paper. "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 other corresponding authors on the paper are Hai Liu of Guangzhou University and Guangyou Fang of the Chinese Academy of Sciences. The other Penn State co-author is Derek Elsworth, the G. Albert Shoemaker Chair and professor of energy and mineral engineering and geosciences. The other authors are Jianhui Li, Xu Meng, Diwen Duan and Haijing Lu of Guangzhou University; Jinhai Zhang and Bin Zhou of the Chinese Academy of Sciences; and Fengshou Zhang of Tongji University in Shanghai, China.
Research Report:Ancient ocean coastal deposits imaged on Mars
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