The Red Planet may have once been significantly wetter than scientists previously believed. A groundbreaking discovery has revealed more than 15,000 kilometers of ancient riverbeds on Mars. This finding fundamentally challenges existing theories about Mars’s early climate.
Researchers focused on Noachis Terra, a vast, relatively underexplored region in Mars’ southern highlands. They studied fluvial sinuous ridges, also known as inverted channels. These features are believed to have formed when sediment deposited by ancient rivers hardened. Over time, the surrounding material eroded, leaving the durable riverbeds exposed. Similar ridges have been observed across various Martian terrains. Their widespread presence suggests that flowing water was once common across this region of Mars.
The new research was led by Adam Losekoot, a PhD student at the Open University. Funded by the UK Space Agency, the findings were presented today at the Royal Astronomical Society’s National Astronomy Meeting 2025 in Durham.
CHALLENGING THE COLD AND DRY THEORY
The findings show that surface water may have remained stable in Noachis Terra. This occurred during the Noachian-Hesperian transition, a period of major geologic and climatic change approximately 3.7 billion years ago.
Historically, Noachis Terra has received less study. This is partly because it holds few valley networks, features traditionally used to infer historical rainfall. This study, however, uses fluvial sinuous ridges as a different form of evidence for ancient surface water.
“Studying Mars, particularly an underexplored region like Noachis Terra, is really exciting,” Losekoot said. “It’s a time capsule that records fundamental geological processes in a way that just isn’t possible here on Earth.”
EVIDENCE OF LONG-LIVED, WIDESPREAD WATER
Losekoot and his team utilized data from three orbital instruments. They used the Context Camera (CTX). They also employed the Mars Orbiter Laser Altimeter (MOLA) and the High Resolution Imaging Science Experiment (HiRISE). These datasets allowed the team to map the locations, lengths, and morphologies of the ridge systems across a wide area.
Many features appear as isolated segments. But, others form extensive systems extending for hundreds of kilometers. These ridges rise tens of meters above the surrounding terrain. Their broad distribution and form suggest that they developed over a geologically significant period. They formed under relatively stable surface conditions.
The spatial distribution and extent of these features strongly indicate precipitation as the water source. This finding contradicts existing theories. These theories suggested that Mars was generally cold and dry. They proposed sporadic, short periods of warming that formed valleys from ice-sheet meltwater.
“Our work is a new piece of evidence,” Losekoot explained, “that suggests that Mars was once a much more complex and active planet than it is now.” The fact that the ridges form extensive interconnected systems suggests that the watery conditions were relatively long-lived. This means Noachis Terra experienced warm and wet conditions for a geologically relevant period.