Today’s Mars is a desert coated in rust-colored dust. But this wasn’t the case 3.7 billion years ago, according to new research presented at the Royal Astronomical Society’s National Astronomy Meeting 2025 in Durham, U.K., suggesting the Red Planet was much more complex – and much more wet – than previously thought.
A team based at The Open University in the U.K. searched for evidence of Fluvial Sinuous Ridges (FSR), also called inverted channels. In total, the researchers discovered more than 15,000 kilometers of these ancient riverbeds – some extending hundreds of kilometers in length.
"Our work is a new piece of evidence that suggests that Mars was once a much more complex and active planet than it is now," Adam Losekoot, a Ph.D. student at The Open University, said in a press release.
Ridge-Like Formations on Mars
FSRs are a geological phenomenon that resemble river channels; but instead of dipping below the surrounding landmass, they rise above it, creating a ridge-like formation. Research suggests that FSRs occur when sediment carried by the river hardens while the softer material that surrounds it erodes, eventually leaving the sediment exposed.
Astronomers frequently look for valleys as signs of ancient water networks on Mars but FSRs can be a handy alternative in their absence.
The researchers focused their attention on the Noachis Terra (or “Land of Noah”), which lies in Mars’ southern highlands. While previous research has shown that FSRs are present elsewhere on the planet, the team suggests that stable water levels existed in the Noachis Terra during the Noachian-Hesperian transition 3.7 billion years ago.
"Studying Mars, particularly an underexplored region like Noachis Terra, is really exciting because it's an environment which has been largely unchanged for billions of years,” said Losekoot in a press release. “It's a time capsule that records fundamental geological processes in a way that just isn't possible here on Earth."
Read More: Evidence of Ancient Beaches Shows Us a Mars With Large, Ice-Free Oceans
Evidence of Precipitation on Mars
According to climate models, it is likely Noachis Terra would have been a region of high precipitation. However, there is limited proof for such predictions in the form of Valley Networks (VN, which is why Losekoot and his team mapped FSRs using the Context Camera (CTX), Mars Orbiter Laser Altimeter (MOLA) and High Resolution Imaging Science Experiment (HiRISE).
Not only were FSRs “common” but in some instances they reached lengths of hundreds of kilometers long and heights of tens of meters above the ground. The widespread nature of these networks suggests precipitation was the most likely source of the water, the study’s authors say. What’s more, these conditions must have been relatively long-lived for the systems to have developed into networks as complex and as deep as they appear to be.
These findings add more weight behind the theory that early Mars was warm and wet for a significantly long period, geologically-speaking – conditions that enabled liquid water to remain a stable feature on the planet for extended periods of time.
In contrast, it (somewhat literally) puts cold water on the theory that Mars has essentially remained cold and dry, with meltwater from ice sheets occasionally and sporadically leaving traces of flowing water.
Read More: Why Is Mars Red? There's a New Story Behind the Red Planet's Coloring
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Royal Astronomical Society’s National Astronomy Meeting 2025. The Fluvial History of Noachis Terra, Mars
Rosie McCall is a freelance writer living in London. She has covered science and health topics for publications, including IFLScience, Newsweek, and Health.
