A ragged geological scar crosses the belly of Mars. Long enough to reach from New York City to Los Angeles, this great rift in the martian crust is named Valles Marineris, or Mariner Valley. It was discovered in 1972 by the Mariner 9 spacecraft. Formed out of several parallel, connecting troughs, Valles Marineris dwarfs Earth's Grand Canyon in every respect, being wider, longer, deeper, and older. It easily earns the title of Grandest Canyon of All.

This mosaic image of Valles Marineris - colored to resemble the martian surface - comes from the Thermal Emission Imaging System (THEMIS), a visible-light and infrared-sensing camera on NASA's Mars Odyssey orbiter. Mars Odyssey was built by Lockheed Martin and the mission is operated by the Jet Propulsion Laboratory.

Built from more than 500 daytime infrared photos, the mosaic shows the whole valley in more detail than any previous composite photo. Despite the valley's huge extent - including its western extension through Noctis Labyrinthus, it reaches some 3,000 kilometers (2,000 miles) long - the smallest details visible in the image are about the size of a football field: 100 meters (328 feet).

This is a reduced size (approximately one fourth the linear pixel density) and cropped (at the bottom) version of the original 23,711 x 11,856 pixel THEMIS mosaic, and has also been adjusted in hue and saturation.