A striking discovery about Mars' past reveals that the planet experienced a much wetter period than previously thought. Scientists have found traces of ancient riverbeds stretching approximately 10,000 miles (around 16,000 km) across the heavily cratered southern highlands of Mars.
Adam Losekoot, a PhD student at Open University, and his team identified these traces using high-resolution images taken by NASA's Mars Reconnaissance Orbiter (MRO) and Mars Global Surveyor satellites.
The examined area covers about 10 million square kilometers — larger than the entire continent of Australia.
Losekoot said, "Water traces have been found many times before on Mars, but this region is special because it was long thought there was no evidence of water here." The discovered river traces are believed to have been fed only by regional rainfall or snowfall.
Researchers tracked geological formations called "fluvial sinuous ridges" in Mars' Noachis Terra region ("Land of Noah"). These formations are sediment layers from ancient riverbeds that hardened over time and became exposed as the surrounding softer ground eroded away.
Some of these glacial rivers are several hundred meters wide and 3 to 4 kilometers long, while larger structures can be over a mile (about 1.6 km) wide. MRO images show some rivers flowing into craters, filling them, then spilling over the crater walls and continuing to flow.
The discovery shows that Mars, 3.7 billion years ago, had a surface very different from today's dry landscape. At that time, the planet had a thicker atmosphere and liquid water on its surface. But as Mars' magnetic field weakened over time, solar winds eroded the atmosphere, causing much of the water to escape into space.
Still, scientists believe that large amounts of water may remain hidden beneath the Red Planet. A study published in April 2025 suggests there is a high possibility of deep underground water reservoirs beyond Mars' icy poles.
These new findings suggest that conditions necessary for life may have been more common on Mars in the past and help improve our understanding of how the planet's water evolved over time.
