Aram Chaos, the lumpy, bumpy floor of an ancient impact crater on Mars, formed as a result of catastrophic melting and outflow of a buried ice lake. A new study combines observations from satellite photos of the 280 kilometre wide and four kilometre deep crater plus models of the ice melting process and resulting catastrophic outflow. Manuel Roda has presented the results at the European Planetary Science Congress (EPSC) at UCL in London.
Chaotic terrains are enigmatic features, stretching up to hundreds of kilometres across, that are distinctive to Mars. The mechanism by which they formed has been poorly understood by scientists.
"About 3.5 billion years ago, the pristine Aram impact crater was partly filled with water ice that was buried under a two-kilometre thick layer of sediment. This layer isolated the ice from surface temperatures, but it gradually melted over a period of millions of years due to the heat released by the planet. The sediment overlying fluid water became unstable and collapsed," said Roda.
The resulting massive expulsion of a hundred thousand cubic kilometres of liquid water was four times the volume of Lake Baikal, the largest freshwater lake on Earth. The water carved a valley of 10 kilometres wide and 2 kilometres deep in about one month and a chaotic pattern of blocks was left in the Aram crater.
"An exciting consequence is that rock-ice units are possibly still present in the subsurface. These never achieved the melting conditions, or melted only a lower thin layer, insufficient to result in a full collapse event. Buried ice lakes testify of Mars rapidly turning into a cold, frozen planet, but with lakes buried in the subsurface. These lakes could provide a potentially favourable site for life, shielded from hazardous UV radiation at the surface," said Roda.
The study was carried out by Roda and colleagues Tanja E. Zegers, Maarten G. Kleinhans and Rob Govers from Utrecht University and Jelmer H.P. Oosthoek of Jacobs University Bremen.
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