Red Planet water may have persisted under seasonal ice.

A new study using the LakeM2ARS model finds that small, seasonal ice covers could have insulated lakes on early Mars and slowed evaporation, helping explain Curiosity’s evidence of past liquid water despite a fainter young Sun.

Rovers have left clear evidence that liquid water once pooled on Mars. A paper by Eleanor Moreland and colleagues in AGU Advances proposes that small, seasonal ice sheets could have insulated those lakes and allowed liquid water to persist. The team built a new model called LakeM2ARS to test how lakes respond to different climates and atmospheric conditions. The idea addresses the long-standing difficulty of explaining surface water when the young Sun was dimmer. Key points: - Curiosity documented deltas, channels and other signs of pooled liquid water around 3.5 billion years ago. - The young Sun was roughly 25% dimmer about 3.6 billion years ago, creating the Faint Young Sun paradox for Mars. - Earlier explanations included brief warming events (from volcanism or impacts) or lakes preserved beneath permanent ice sheets. - LakeM2ARS simulations showed that largely warm, ice-free conditions increase evaporation and dry lakes quickly, while seasonal ice cover reduces evaporation and can allow liquid water to remain during warmer seasons. - The lack of features associated with permanent ice (for example, dropstones and frost wedges) in Gale Crater is consistent with seasonal rather than permanent ice cover. Summary: The study offers a middle-ground explanation that reconciles rover observations with a generally cold early Mars by showing how seasonal ice could slow evaporation without leaving the marks expected under permanent ice. The LakeM2ARS model can be applied to other sites, including Jezero Crater where Perseverance operates, to further test how widespread this mechanism might have been.