The metal balls in this image are only two millimeters in diameter (0.078 inches). The image, which covers an area about 0.5 inches long and is illuminated by four white light-emitting diodes, was taken by NASA's latest and most advanced camera:
It's the Mars Hand Lens Imager (MAHLI), a device capable of capturing images with a resolution of 15.4 microns per pixel. That's about twice as high as the resolution on Mars Rovers Spirit and Opportunity. The device will fly on NASA's Mars Science Laboratory mission in late 2011, attached to Mars Rover Curiosity's articulated arm.
Using this camera, geologists would be able to get closer than ever to every rock or sand pit, analysing the images to study their composition as if they were on the planet itself. The image above was taken in a sand dune near Christmas Lake, Oregon. From it, geologist know that "the largest white grains are pumice fragments and the dark black and grey grains are fragments of basalt. Nearly transparent, slightly yellow crystals are feldspars. The crystals and pumice were erupted by Mount Mazama in its terminal explosion about 7700 years ago; the volcano is known today as Crater Lake."
Zoom in to see the actual size or go to NASA to download the 1600x1200 pixel version. [NASA]