For years, scientists have faced a puzzling contradiction about Mars.
On one hand, the planet is covered with ancient lake beds, shorelines, and sediment layers that clearly show liquid water once flowed across its surface.
On the other hand, climate models suggest that early Mars was far too cold to keep water liquid for long.
A new study now offers a compelling solution: thin, seasonal ice may have protected lakes on Mars, allowing them to stay liquid for decades even in freezing conditions.
The research was led by scientists at Rice University and published in the journal AGU Advances.
Using a climate model adapted specifically for Mars, the team found that small lakes near the planet’s equator—such as those in Gale Crater—could have survived under a thin layer of ice that formed and melted with the seasons.
Rather than freezing solid, these lakes would develop a shallow ice cover during colder periods. This ice acted like a blanket, insulating the water below and slowing evaporation.
When warmer seasons returned, sunlight could pass through the thin ice and gently warm the lake again.
As long as overall climate conditions stayed relatively stable, the lakes could persist for decades, even though air temperatures were often well below freezing.
“This helps explain something that never quite added up,” said Eleanor Moreland, a graduate student at Rice University and lead author of the study.
Scientists have seen clear evidence of long-lasting lakes on Mars, but not the thick, permanent ice sheets that should exist if those lakes had been frozen solid. Thin, seasonal ice would leave little trace behind, matching what Mars rovers observe today.
To explore this idea, the researchers adapted a powerful Earth-based climate modeling tool called Proxy System Modeling. On Earth, scientists use natural records like tree rings or ice cores to reconstruct ancient climates. Mars has no trees or glaciers that preserve such records, so the team relied instead on rock and mineral data collected by rovers.
They focused on data from NASA’s Curiosity rover, which has been exploring Gale Crater for more than a decade. By combining these observations with simulations of early Mars’ atmosphere—which was rich in carbon dioxide and received weaker sunlight than Earth—the researchers rebuilt what Martian lakes might have been like about 3.6 billion years ago.
The team ran 64 different simulations using a new model they developed called LakeM2ARS. Each simulation tested whether a lake inside Gale Crater could remain liquid for 30 Martian years, which is roughly 56 Earth years. Some lakes froze completely during colder periods. Others, however, remained stable beneath thin ice, barely changing in depth over decades.
“The ice behaves like a natural thermal shield,” explained Kirsten Siebach, a co-author of the study. It protects the lake in winter while still allowing melting and warming in summer. Because the ice is thin and temporary, it wouldn’t create obvious glacial features, helping explain why Mars lacks clear signs of permanent ice cover around ancient lakes.
This finding reshapes how scientists think about early Mars. It suggests that the planet did not need a warm, Earth-like climate to support long-lasting surface water. Instead, even a cold Mars could have hosted stable lakes—conditions that may have been suitable for microbial life.
The researchers plan to apply their model to other Martian basins to see if similar lakes could have existed elsewhere on the planet. They also want to explore how changes in Mars’ atmosphere or underground water flow may have influenced lake stability.
If thin ice protected lakes across much of early Mars, it strengthens the idea that the planet once had widespread, long-lived liquid water. That possibility makes ancient Mars an even more intriguing place in the search for past life—and shows that sometimes, the key to survival is not warmth, but protection.
