**Scientists Discover Convincing Signs of an Ancient Ocean on Mars**
For years, researchers have uncovered remnants of dried streams, lakes, and gullies on Mars, pointing to a historical presence of water. Nonetheless, substantiating the existence of a vast ocean has posed a significant challenge.
A recent study utilizing data gathered from China’s now-dormant Zhurong rover provides compelling evidence of a large, ancient ocean. Unlike transient lakes that arise from melted ice, this water body would have functioned as a grand sea, covering nearly one-third of the planet’s surface.
Published in the *Proceedings of the National Academy of Sciences*, this research indicates that Mars endured a warm and wet climate spanning tens of millions of years. Such conditions would have heightened the potential for habitability, even if life never actually developed there. Benjamin Cardinas, a sediment geologist at Penn State and a coauthor of the study, noted that the conditions along these ancient Martian coastlines might have closely resembled those where life first emerged on Earth.
### Insights from China’s Zhurong Rover
The conclusions are grounded in data from the Zhurong rover, part of China’s Tianwen-1 mission, which landed on Mars in May 2021. The six-wheeled rover explored Utopia Planitia, an area situated far from NASA’s Curiosity and Perseverance rovers, and was also the landing site for the U.S. Viking 2 lander in 1976.
Collaborative efforts between Chinese and U.S. scientists often face hurdles due to the 2011 Wolf Amendment, which restricts NASA’s collaboration with China over technology security concerns. However, several U.S. researchers contributed to the study without federal support, and China released the rover data publicly as mandated for publication.
### Subsurface Indications of an Ocean
Earlier satellite imagery suggested that Utopia Planitia may have once contained water, but the theory remained unverified due to insufficient underground evidence. Coastline-like features appeared at varying elevations, leading to uncertainty over their origins—whether shaped by water, lava, wind, or ancient rivers.
Before concluding its operations in December 2022, Zhurong traveled approximately a mile across the Martian terrain, gathering significant data. A crucial tool was its ground-penetrating radar, which transmitted radio waves underground to identify different layers of rock and soil.
This data showcased sloping underground formations reminiscent of those created by waves depositing sediment along Earth’s beaches. These ancient shorelines extended nearly a mile and were buried between 30 to 115 feet below the Martian surface.
Michael Manga, a geoscientist at UC Berkeley and coauthor of the study, explained that developing such extensive beach deposits on Earth requires hundreds of thousands to millions of years. If similar mechanisms occurred on Mars, it implies that the ocean persisted for a considerable duration.
### Insights on Mars’ Water Cycle
The findings imply that Mars once had a sophisticated water cycle, with tides, standing water, and rivers supplying sediment to the ocean over time.
Manga, a longstanding advocate for the ocean hypothesis, expressed enthusiasm over the Zhurong data. “Just the idea that a rover can traverse Mars, explore the surface, and examine the underground is astonishing,” he said. “But to observe something structured and consistent across such a vast area was incredibly exciting.”
NASA’s Perseverance rover has also recorded sloping underground layers in Jezero Crater, a previous lakebed. However, those structures may have been formed by either water or magma. Notably, the Jezero materials demonstrated high electrical charge retention, possibly indicating the presence of volcanic rock, while the Utopia Planitia materials exhibited low electrical charge retention, hinting at a mix of sand and pebbles akin to Earth’s shorelines.
### A Varied Martian Narrative
The contrasting findings from Zhurong and Perseverance underscore the variety of Martian environments. Perseverance is located about 3,000 miles from Zhurong, further than the distance between New York and Los Angeles. Meanwhile, investigations at Gale Crater, where NASA’s Curiosity rover operates, suggest that region was icy and salty—possibly too extreme for life to emerge, at least on the surface.
“It’s not surprising that distinct regions of Mars reveal different narratives,” Cardinas remarked. “Areas of Mars may have varied significantly at different points in time.”
### The Enigma of Mars’ Vanished Water
While this study bolsters the argument for a historic Martian ocean, it simultaneously raises further questions—most notably, what happened to all the water? Did it freeze beneath the surface, form ice sheets at the poles, or escape into space? Unraveling this mystery could aid scientists in understanding planetary evolution and whether similar transformations might occur on Earth.
Another aspect to ponder is how Mars’ lower gravity—approximately 62% less than Earth’s—may have influenced the creation of beaches. Scientists remain uncertain about the extent to which this could have affected the formation.