Researchers from Rice University have utilized a climate model tailored for Mars to investigate the possibility of lakes surviving in locations like Gale Crater, situated near the planet's equator. Their findings indicate that lakes could potentially remain liquid beneath a thin layer of seasonal ice for decades, provided that the overall climate conditions remain stable. This discovery addresses a longstanding query in Mars exploration, as geological formations indicative of flowing or standing water are widespread across the planet, despite many climate models suggesting that early Mars was too frigid to sustain liquid water.
The study, featured in AGU Advances, presents a fresh perspective on how lakes might have existed without requiring a warm climate, explaining the remarkable preservation of ancient Martian lake beds.
"Observing ancient lake basins on Mars without definitive signs of thick, enduring ice led me to question whether those lakes could retain water beyond a single season in a colder climate," remarked Eleanor Moreland, a graduate student at Rice and the study's lead author. "When our new model began to reveal lakes that could persist for decades with just a thin, seasonal ice layer, it was thrilling to consider that we might finally have a physical explanation that aligns with our observations of Mars today."
Adapting Earth Climate Models for Mars
To tackle this issue, the research team modified a climate modeling framework known as Proxy System Modeling, initially developed by Earth climate researcher Sylvia Dee to reconstruct ancient climates using indirect indicators like tree rings or ice cores.
Given that Mars lacks familiar climate markers, the team relied on data gathered from Mars rovers. Rock formations and mineral deposits provided a substitute for climate records, enabling the researchers to deduce past conditions.
Over several years, the researchers adjusted the lake model to reflect Mars as it was approximately 3.6 billion years ago, considering factors such as diminished sunlight, a carbon dioxide-rich atmosphere, and unique seasonal variations.
Employing the new Lake Modeling on Mars with Atmospheric Reconstructions and Simulations (LakeM2ARS) model, the team conducted 64 test scenarios based on measurements from NASA's Curiosity rover in Gale Crater and existing Mars climate simulations.
Each scenario simulated a hypothetical lake within the crater for 30 Martian years, equivalent to around 56 Earth years, allowing the researchers to evaluate whether lakes could feasibly remain liquid under varying conditions.
"It was fascinating to explore how a lake model designed for Earth could be adapted for another planet, although this process involved significant debugging when we had to adjust parameters such as gravity," stated Dee, an associate professor of Earth, environmental, and planetary sciences and co-author of the study.
"We were both surprised and encouraged by how sensitively the model reacted to factors like atmospheric pressure and temperature seasonality. This indicates that with creativity and experimentation, Earth-based models can produce realistic climate scenarios for Mars."
Thin Ice as a Natural Insulator
The simulations yielded diverse outcomes depending on the conditions. In certain scenarios, lakes froze completely during colder seasons, while in others, the water remained liquid beneath a thin ice cover instead of freezing entirely.
This thin ice layer played a vital role, acting as an insulating barrier that reduced evaporation and water loss while still permitting sunlight to warm the lake during the warmer months.
Due to this seasonal cycle, some modeled lakes displayed minimal changes in depth over decades, suggesting their stability even when average air temperatures hovered below freezing.
"This seasonal ice cover functions as a natural blanket for the lake," noted Kirsten Siebach, an associate professor of Earth, environmental, and planetary sciences and co-author of the study.
It insulates the water in winter while allowing it to melt in summer, Siebach explained. "As the ice is thin and temporary, it would leave little evidence, which may clarify why rovers haven't detected clear signs of permanent ice or glaciers on Mars," she added.
Rethinking Water on a Cold Mars
The findings imply that early Mars could have supported long-lasting lakes without necessitating consistently warm conditions. This challenges previous assumptions that surface water on Mars could only exist during prolonged warm periods.
If lakes were safeguarded by seasonal ice rather than buried under thick permanent ice, many enigmatic features on Mars become more comprehensible. Preserved shorelines, layered sediments, and mineral deposits may all represent stable lakes that persisted despite a cold climate.
Implications for Future Mars Research
The researchers aim to apply the LakeM2ARS model to other Martian basins to investigate whether similar lakes could have existed elsewhere on the planet. They also seek to examine how variations in atmospheric composition or groundwater flow may have affected lake stability over time.
"If similar patterns are observed across the planet, the results would bolster the notion that even a relatively cold early Mars could sustain year-round liquid water, a crucial element for environments conducive to life," Moreland concluded.
The study also includes contributions from Rice undergraduate student Nyla Hartigan, Michael Mischna from the Jet Propulsion Laboratory at the California Institute of Technology, James Russell from Brown University, and Grace Bischof and John Moores from York University. The Rice Faculty Initiative Fund and the Canadian Space Agency provided support for this research.