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Nasa has sent its Curiosity rover to investigate a mysterious set of rocks they have dubbed the 'pink cliffs'

They form a strange ledge that Nasa is keen to examine, and possibly drill into.

It is hoped the unique formation could give clues to how Mars formed.

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This small ridge, about 3 feet (1 meter) long, appears to resist wind erosion more than the flatter plates around it, and has been dubbed the 'pink cliff'. This image combines several frames , and the colour has been altered to resemble how it would appear on Earth.

This view is a mosaic of exposures acquired by Curiosity's Mast Camera (Mastcam) shortly before a two-week walkabout up the outcrop, scouting to select which targets to examine in greater detail during a second pass. 

This small ridge, about 3 feet (1 meter) long, appears to resist wind erosion more than the flatter plates around it. 

Such differences are among the rock characteristics that NASA's Curiosity Mars rover is examining at selected targets at the base of Mount Sharp.

The ridge pictured here, called 'Pink Cliffs,' is within the 'Pahrump Hills' outcrop forming part of the basal layer of the mountain. 

'We see a diversity of textures in this outcrop -- some parts finely layered and fine-grained, others more blocky with erosion-resistant ledges,' said Curiosity Deputy Project Scientist Ashwin Vasavada of NASA's Jet Propulsion Laboratory, Pasadena, California. 

'Overlaid on that structure are compositional variations. Some of those variations were detected with our spectrometer. 

Others show themselves as apparent differences in cementation or as mineral veins. 

'There's a lot to study here.'

The pink cliffs image combines several frames taken with the Mastcam on Oct. 7, 2014, the 771st Martian day, or sol of Curiosity's work on Mars. 

The colour has been approximately white-balanced to resemble how the scene would appear under daytime lighting conditions on Earth.

It comes as Nasa's Curiosity Mars rover completed a reconnaissance 'walkabout' of the first outcrop it reached at the base of the mission's destination mountain. 

A wheel track cuts through a windblown ripple of dusty sand in this Nov. 7, 2014, image from the Mastcam on NASA's Curiosity rover. The view spans about four feet across. This experiment was planned for yielding a view of the inside of the ripple for assessment of particle sizes and composition. One motive for this experiment was to learn why some ripples that Curiosity drove into earlier this year were more difficult to cross than anticipated.

Exposed layers on the lower portion of Mount Sharp are expected to hold evidence about dramatic changes in the environmental evolution of Mars. 

That was a major reason NASA chose this area of Mars for this mission. 

The lowermost of these slices of time ascending the mountain includes a pale outcrop called 'Pahrump Hills.' 

It bears layers of diverse textures that the mission has been studying since Curiosity acquired a drilled sample from the outcrop in September.

In its first pass up this outcrop, Curiosity drove about 360 feet (110 meters), and scouted sites ranging about 30 feet (9 meters) in elevation. It evaluated potential study targets from a distance with mast-mounted cameras and a laser-firing spectrometer.

During a second pass up the outrcrop, the mission is using a close-up camera and spectrometer on the rover's arm to examine selected targets in more detail. 

The second-pass findings will feed into decisions about whether to drill into some target rocks during a third pass, to collect sample material for onboard laboratory analysis.

This patch of Martian bedrock, about 2 feet (70 centimeters) across, is finely layered rock with some pea-size rocks. It lies near the lowest point of the 'Pahrump Hills' outcrop of Mount Sharp, where Nasa hopes researchers will find clues about the planet's past.

'The variations we've seen so far tell us that the environment was changing over time, both as the sediments were laid down and also after they hardened into bedrock,' Vasavada said. 

'We have selected targets that we think give us the best chance of answering questions about how the sediments were deposited -- in standing water? flowing water? sand blowing in the wind? -- and about the composition during deposition and later changes.'  

Curiosity landed on Mars in August 2012, but before beginning the drive toward Mount Sharp, the rover spent much of the mission's first year productively studying an area much closer to the landing site, but in the opposite direction. 

The mission accomplished its science goals in that Yellowknife Bay area. 

Analysis of drilled rocks there disclosed an ancient lakebed environment that, more than three billion years ago, offered ingredients and a chemical energy gradient favorable for microbes, if any existed there.

Curiosity spent its second year driving more than 5 miles (8 kilometers) from Yellowknife Bay to the base of Mount Sharp, with pauses at a few science waypoints.