Illustration depicts a lake of water partially filling Mars' Gale Crater, receiving runoff from snow melting on the crater's northern rim NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS

A new interpretation of the findings in the Gale Crater on Mars suggests that the ancient climate on the planet could have sustained many lakes in the past.

It challenges the view that water was an underground commodity and warm, wet conditions on the Red Planet transient.

Observations by Mars Rover Curiosity indicate Mt Sharp was built with sediments deposited in a large lake bed a million years ago. The rock layers – alternating between lake, river and wind deposits – are proof of the constant filling and evaporation of a large and long-lasting Martian lake, says Nasa.

The five km tall mountain made of rocks stands in the centre of the Gale Crater.

"A more radical explanation is that Mars' ancient, thicker atmosphere raised temperatures above freezing globally, but so far we don't know how the atmosphere did that," said Ashwin Vasavada, Curiosity deputy project scientist at NASA's Jet Propulsion Laboratory in Pasadena.

Curiosity currently is at a height of 500 feet on Mount Sharp, studying the Murray sedimentary layers.
In repeated cycles, rivers carried sand and silt to the lake, forming deltas at river mouths. This cycle occurred over and over again.

Gradually the sediments hardened to rock while layers of it were piled by the wind to form a mountain.

The wind also carved away the material between the crater's perimeter and what is now the edge of the mountain, according to the hypothesis.

"We are making headway in solving the mystery of Mount Sharp," said Curiosity Project scientist John Grotzinger of the California Institute of Technology in Pasadena, California. "Where there's now a mountain, there may have once been a series of lakes."

From 2012 when it landed on Mars, the rover has covered 8 kilometers to the base of Mount Sharp. On the way it has uncovered clues about the changing shape of the crater floor.

"We found sedimentary rocks suggestive of small, ancient deltas stacked on top of one another," said Curiosity science team member Sanjeev Gupta of Imperial College in London. "Curiosity crossed a boundary from an environment dominated by rivers to an environment dominated by lakes."

Images taken by Curiosity earlier too have shown evidence of rocks smoothed by water as also sedimentary rocks in the valley suggesting the valley once was a freshwater lake. Presence of iron oxide suggests the presence of water on Mars for longer periods than believed. Study of meteorites from Mars too strengthened the case.

This evenly layered rock photographed by the Mast Camera (Mastcam) on NASA's Curiosity Mars Rover on 7 August 2014, shows a pattern typical of a lake-floor sedimentary deposit not far from where flowing water entered a lake NASA/JPL-Caltech/MSSS