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A series of huge cracks etched across crater basins on Mars were caused by lakes that have since evaporated, a new study concludes.The cracks were initially thought to have been merely a byproduct of thermal contractions in the Martian permafrost. But a closer examination revealed the cracks were too big for that explanation. Cracks caused by thermal contraction have a maximum diameter of roughly 213 feet (65 meters), according to analytical models. "They resembled the desiccation cracks that we see on Earth in dried up lakes, said M. Ramy El Maarry of the Max Planck Institute for Solar System Research. "These are the same type of patterns you see when mud dries out in your back yard, but the stresses that build up when liquids evaporate can cause deep cracks and polygons on the scale I was seeing in the craters."
The average diameter of the cracks in the survey was between 43 miles and 87 miles (70 to 140 kilometers), with a width ranging from 3 to 33 feet (1 to 10 meters). "When a meteorite impacts with the Martian surface, the heat can melt ice trapped beneath the Martian crust and create what we call a hydrothermal system. Liquid water can fill the crater to form a lake, covered in a thick layer of ice. Even under current climatic conditions, this may take many thousands of years to disappear, finally resulting in the desiccation patterns," explained El Maarry.
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