With NASA's Spirit rover safely on Mars and ready to poke around, secrets of the red planet are sure to unravel in coming months. But other places on Mars will likely remain mysterious until researchers can take closer looks at more and more of the planet.

This Mars Global Surveyor image, released in December, shows an ancient, unnamed valley in the Xanthe Terra region, located near 3.3°S, 54.9°W.

This valley might have been a conduit for flowing water, according to scientists at Malin Space Science Systems, which operates the spacecraft's camera. But there is no way to be certain, they said, because the valley is so old that none of its original features have been preserved. Bright, windblown ripples are now found on the valley floor.

The image covers an area 1.9 miles (3 kilometers) wide. Sunlight illuminates the scene from the left.

Credit: NASA/JPL/Malin Space Science Systems