Ten times longer than the Grand Canyon, and three times as deep, the Valles Marineris (The Mariner Valley) cuts through the surface of Mars. This grandest canyon in the Solar System stretches 4,000 km (2,500 miles) across the Red Planet — nearly covering a quarter of the circumference of that ruddy world. Now, images released on Christmas Day, utilizing the HiRISE (High Resolution Imaging Science Experiment) onboard the Mars Reconnaissance Orbiter, show this mighty rift in stunning detail. Where’s the river? There was supposed to be a river More than five million years ago, the Grand Canyon in Arizona was…

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