There are numerous geological traces of ancient lakes and rivers on Mars. Still, it is unclear how these bodies of water were able to survive despite a thin atmosphere and cold temperatures. Now a new model offers a possible answer – at least for some of the lakes of early Mars. Accordingly, a thin layer of winter ice could have helped keep the water in Martian lakes liquid despite frosty conditions. The thin layer of ice allowed warming sunlight to pass through, but insulated the lake water from the cold and slowed down water loss through evaporation, as planetary scientists report. In their simulation, the shallow lake in Mars’ Gale Crater remained intact for more than 100 years despite the cold. If this is confirmed for other Martian lakes, it could explain how these waters were preserved despite freezing conditions.
Mars was warmer in its early days than it is today and may have had liquid water in the form of lakes and rivers – this seems to be indicated by sediments and riverbed-like landforms. However, it is controversial how much water there was once on the Red Planet and how long it existed. The thin atmosphere, the planet’s small size and unclear data about its past climate make some planetary scientists doubt that our neighboring planet was ever a warm, life-friendly world. Instead, many Mars climate models suggest that Mars was rather dry and cold even in its early days more than 3.6 billion years ago. Nevertheless, there are numerous geological traces of ancient bodies of water on Mars, including evidence of rivers, lakes and perhaps even an ocean.
Development of a Martian lake in the model
The NASA rover “Curiosity” also discovered clear evidence of a former lake in the crater during its exploration trips in the Martian Gale Crater. Multiple layers of fine-grained sediment suggest that this lake was at least four, but probably more than ten, meters deep and existed for 1,000 to 10,000 years. “Some studies suggest that liquid water would last longest in Gale Crater Lake if the lake were covered with perennial ice three to ten meters thick adjacent to a glacier,” explain Eleanor Moreland of Rice University and her colleagues. However, such a thick, permanent layer of ice would have left clearly visible traces in the sedimentary layers of that time. Moreland and her team therefore favor a different scenario: a thin, seasonal ice cover of the Martian lakes. “If that “If the ice layer of these lakes was only around 0.5 to two meters thick and melted and froze every year, this would hardly have caused any obvious stratigraphic traces,” they explain.
To find out under what conditions the Martian lake was able to survive for so long, Moreland and her colleagues reconstructed it in a model simulation. To do this, they adapted a model developed for terrestrial conditions that was originally intended to reconstruct past climate conditions using indirect evidence such as tree rings or ice cores. Instead, the team used measurement data from the Mars rover and Mars orbiter probes as the basis for their Mars version. In their 64 model runs, they simulated the development of a hypothetical lake in Gale Crater over 30 Martian years under various early Martian conditions. In addition to a thin carbon dioxide atmosphere, weak sunlight and varying seasons, they also took into account different salinities and climates.
Winter ice as an insulating layer
The simulations showed that there were indeed some conditions under which the water in the lake in Gale Crater could remain liquid. A thin, seasonal ice cover on the lake actually played a key role. “When our model showed that such lakes could exist for decades with just a thin, seasonally disappearing layer of ice, I was thrilled,” says Moreland. “We may have finally found a physical mechanism that agrees with the observation data from Mars.” In the simulations, Gale Crater Lake was preserved when covered by a layer of ice in winter. “This seasonal ice cover behaves like a natural blanket for the lake,” says senior author Kirsten Siebach of Rice University. The ice insulates the water in winter but allows enough sunlight to pass through to warm it. At the same time, the ice layer slowed down the evaporation of the lake water, meaning that the lake hardly lost any volume despite low rainfall, as the team explains.
According to the researchers, their results suggest that lakes close to the Martian equator were able to exist for decades and probably much longer thanks to such a thin layer of seasonal ice. This could explain how such Martian lakes persisted for extended periods of time when average air temperatures were below freezing much of the time. “If similar patterns emerge across the planet, the results would support the idea that even a fairly cold early Mars could have hosted liquid water year-round – an essential requirement for life-friendly environments,” says Moreland.
Source: Eleanor Moreland (Rice University, Houston) et al., AGU Advances, doi: 10.1029/2025AV001891