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Curiosity unravels the mystery of water on Mars

Jenny Winder, News Writer
Dec 9, 2014, 4:51 UTC

Sen—NASA’s Curiosity Rover has gathered evidence that Mars' Mount Sharp was built by sediments deposited in a large lake bed over tens of millions of years. This supports the theory that ancient Mars maintained a climate that could have produced long-lasting lakes at many locations on the Red Planet, lakes that possibly supported microbial life.

"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. “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."

Mount Sharp stands 3 miles (5 kilometres) tall, its lower flanks exposing layers of rock that alternate between lake, river and wind deposits. This suggests the repeated filling and evaporation of a Martian lake much larger and longer-lasting than any previously examined close-up.


The region oscillated between wet and dry periods, accumulating sediment. Image credit: NASA/JPL-Caltech

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

Curiosity is currently investigating the lowest sedimentary layers of Mount Sharp, a section of rock 500 ft (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 in a repeating cycle.

"The great thing about a lake that occurs repeatedly, over and over, is that each time it comes back it is another experiment to tell you how the environment works," Grotzinger said. "As Curiosity climbs higher on Mount Sharp, we will have a series of experiments to show patterns in how the atmosphere and the water and the sediments interact. We may see how the chemistry changed in the lakes over time. This is a hypothesis supported by what we have observed so far, providing a framework for testing in the coming year."

The crater would have filled to a height of a few hundred yards and the sediments hardened into rock, the accumulated layers of sediment were sculpted into a mountainous shape by wind erosion that carved away the material between the crater perimeter and what is now the edge of the mountain.


Sedimentation and Erosion in Gale Crater. Sediments transported toward the center of the crater in alluvial fans, deltas, and wind-blown drifts (yellow) Water pooled in lakes where sediments settled out (brown). Later erosion of previously deposited sedimentary layers occurred. Image credit: NASA/JPL-Caltech

On the 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.

"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."

Modeling of the ancient climate has yet to identify the conditions that could have produced long periods warm enough for stable water on the surface.

"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.


This oblique view of Mount Sharp, is derived from a combination of elevation and imaging data from three Mars orbiters. Image credit: NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS

Curiosity Rover Report: The Making of Mount Sharp. Credit: NASA Jet Propulsion Laboratory