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Mars rover sees its own shadow

NASA / JPL-Caltech / Cornell / ASU

NASA's Opportunity rover catches its own late-afternoon shadow in a view looking eastward across Endeavour Crater on Mars. Endeavour measures 14 miles across, encompassing a crater with about as much area as the city of Seattle. The colors in this picture have been tweaked to exaggerate surface differences.

NASA's Opportunity rover can't really take a full-frontal picture of itself on Mars, but catching its own shadow on camera is the next best thing. And if you can get a breathtaking view of Endeavour Crater in the background, so much the better.

This view combines about a dozen separate images taken by Opportunity's panoramic camera in early March, while the rover was biding its time on Endeavour's western rim. At the time, the solar-powered rover was in stationary, low-energy mode due to the Martian winter. But since the images for this mosaic were collected, Opportunity has resumed its drive and is currently investigating a patch of windblown Martian dust nearby.

Eventually, Opportunity will head for a spot known as Cape Tribulation to look for special types of clay minerals known as phyllosilicates. If such minerals are found, studying the deposits could provide fresh insights into the role that water played in Mars' ancient past.

The picture reflects the scene at 4:30 to 5 p.m. on a Martian afternoon, with the colors enhanced to exaggerate differences in surface composition. That's why the far reaches of Endeavour Crater's basin have a bluish tinge. In natural color, the vista would have a more uniform reddish tone.

And while we're on the subject of color, check out the knobby protuberance at lower left. That's the rover's sundial. The device isn't used so much to tell the time as to calibrate the panoramic camera's color balance. Patches of color and circles of grayscale help the rover operators back on Earth figure out how to match the colors to what the eye would see. Unfortunately, the color-calibrating "Marsdial" isn't as helpful as it might be, because it's covered with reddish dust — like the rest of the solar panels in the foreground.

To find out what the Marsdial looks like when it's cleaned up, and to get a better sense of how it's used, check out this explanation from Cornell University's Athena team.

NASA sent Opportunity and its twin, Spirit, to opposite sides of Mars in January 2004, with the expectation that their missions would last for 90 days. Both rovers were crazy overachievers, and although Spirit gave up the ghost a year or two ago, Opportunity is still going strong. Soon it will no longer be alone: In August, NASA's Curiosity rover is due to be dropped onto the Martian surface for at least a couple of years of work on the Red Planet.

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Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.