See pics: NASA Mars rover captures images of ancient valley carved by water

NASA's Mars rover has beamed back images of an ancient valley that may have been carved by flowing water on the inner slope of a vast crater's rim.

As NASA's Mars Exploration Rover Opportunity approached the upper end of "Perseverance Valley" in early May - the main destination of its extended mission - images from its cameras began showing parts of the area in greater resolution than what can be seen in images taken from orbit above the red planet.

"The science team is really jazzed at starting to see this area up close and looking for clues to help us distinguish among multiple hypotheses about how the valley formed," said Opportunity Project Scientist Matt Golombek of NASA's Jet Propulsion Laboratory in the US.

The process that carved Perseverance Valley into the rim of Endeavour Crater billions of years ago has not yet been identified.

It may have been carved by flowing water, or a debris flow in which a small amount of water lubricated a turbulent mix of mud and boulders. Even a drier process, such as wind erosion, may have made such carvings possible.

The mission's main objective with Opportunity at this site is to assess which possibility is best supported by the evidence still in place.

The upper end of the valley is at a broad notch in the crest of the crater rim. The rover team's plan for studying the area begins with taking sets of images of the valley from two widely separated points at that dip in the rim.

This long-baseline stereo imaging will provide information for extraordinarily detailed 3D analysis of the terrain.

The valley extends down from the rim's crest line into the crater, at a slope of about 15 to 17 degrees for a distance of about two football fields.

"The long-baseline stereo imaging will be used to generate a digital elevation map that will help the team carefully evaluate possible driving routes down the valley before starting the descent," said Opportunity Project Manager John Callas of JPL.

Reversing course back uphill when partway down could be difficult, so finding a path with minimum obstacles will be important for driving Opportunity through the whole valley.

Researchers intend to use the rover to examine textures and compositions at the top, throughout the length and at the bottom, as part of investigating the valley's history.

While the stereo imaging is being analysed for drive- planning, the team plans to use the rover to examine the area immediately west of the crater rim at the top of the valley.

"We expect to do a little walkabout just outside the crater before driving down Perseverance Valley," Golombek said.