Evidence on Mars of huge ancient lake say scientists

Evidence of a huge ancient lake covering more than a million square kilometres has been discovered on Mars.

Early in the planet's history, about 3.5 billion years ago, the 1,100 metre deep lake would have contained almost 500,000 cubic kilometres of water.

At some stage the lake overflowed and cut through a weak spot in its perimeter, the scientists believe.

Water surging through the gap formed the Ma'adim Vallis valley, which is between eight and 15 kilometres wide and one of the largest valleys in the Martian highlands.

Originally it had been thought the valley was created by a groundwater source.

Finely detailed images from the Mars Global Surveyor spacecraft revealed the first clues about the lake.

Researchers from the Smithsonian Institution in Washington DC and the University of Virginia at Charlottesville reported the findings in the journal Science.

They wrote: "The interior morphology of this source basin, including likely shoreline features following topographic contours, suggests that Ma'adim Vallis was created through catastrophic overflow of a 1,100,000 square kilometre highland lake."