The Curiosity rover captured this image of Mount Sharp. NASAMount Sharp on Mars was built by sediments deposited in a large lake bed over tens of millions of years, according to observations by NASA's Curiosity Rover.
'This interpretation of Curiosity's finds in Gale Crater suggests ancient Mars maintained a climate that could have produced long-lasting lakes at many locations on the Red Planet,' the agency said in a statement.
'If our hypothesis for Mount Sharp holds up, it challenges the notion that warm and wet conditions were transient, local, or only underground on Mars,' said Ashwin Vasavada, Curiosity deputy project scientist at NASA's Jet Propulsion Laboratory in Pasadena.
'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.'
Why this layered mountain sits in a crater has been a challenging question for researchers. Mount Sharp stands about five kilometres tall, its lower flanks exposing hundreds of rock layers. The rock layers - lternating between lake, river and wind deposits - bear witness to the repeated filling and evaporation of a Martian lake much larger and longer-lasting than any previously examined close-up.
'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.'
Curiosity currently is investigating the lowest sedimentary layers of Mount Sharp, a section of rock 150 metres high dubbed the Murray formation. Rivers carried sand and silt to the lake, depositing the sediments at the mouth of the river to form deltas similar to those found at river mouths on Earth. This cycle occurred over and over again.
On the 8-kilometre journey from Curiosity?s 2012 landing site to its current work site at the base of Mount Sharp, the rover uncovered clues about the changing shape of the crater floor during the era of lakes.
'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.'
Despite earlier evidence from several Mars missions that pointed to wet environments on ancient Mars, modelling of the ancient climate has yet to identify the conditions that could have produced long periods warm enough for stable water on the surface.
NASA's Mars Science Laboratory Project uses Curiosity to assess ancient, potentially habitable environments and the significant changes the Martian environment has experienced over millions of years. This project is one element of NASA's ongoing Mars research and preparation for a human mission to the planet in the 2030s.
'Knowledge we're gaining about Mars' environmental evolution by deciphering how Mount Sharp formed will also help guide plans for future missions to seek signs of Martian life,' said Michael Meyer, lead scientist for NASA's Mars Exploration Program at the agency's headquarters in Washington.
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