According to a team of planetary scientists led by Dr Manuel Roda from the Utrecht University, a huge impact crater on Mars known as Aram Chaos formed as a result of catastrophic melting and outflow of a buried ice lake.

Chaotic terrains are enigmatic features, stretching up to hundreds of kilometers across, that are distinctive to Mars. The mechanism by which they formed has been poorly understood by scientists.

Aram Chaos measures about 280 km (170 miles) across and 4 km (2.5 miles) deep. It lies at the eastern end of the large canyon Valles Marineris.

The new study, reported on Friday at the 2013 European Planetary Science Congress in London, United Kingdom, combines observations from satellite photos of the crater and models of the ice melting process and resulting catastrophic outflow.

“About 3.5 billion years ago, the pristine Aram impact crater was partly filled with water ice that was buried under a 2-km thick layer of sediment,” Dr Roda said.

“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.”

The resulting massive expulsion of a hundred thousand cubic kilometers of liquid water was four times the volume of Lake Baikal, the largest freshwater lake on Earth.

The water carved a valley of 10 km (6.2 miles) wide and 2 km (1.2 miles) 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,” Dr Roda said.

“These lakes could provide a potentially favorable site for life, shielded from hazardous UV radiation at the surface.”

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Bibliographic information: M. Roda et al. 2013. Sub-ice lake scenario for Chaotic Terrains on Mars. EPSC Abstracts vol. 8, EPSC2013-194