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How large is Valles Marineris compared with the Grand Canyon?
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Mars
An especially serene view of Mars (Tharsis side), a composite of images taken by the Mars Global Surveyor spacecraft in April 1999. The northern polar cap and encircling dark dune field of Vastitas Borealis are visible at the top of the globe. White water-ice clouds surround the most prominent volcanic peaks, including Olympus Mons near the western limb, Alba Patera to its northeast, and the line of Tharsis volcanoes to the southeast. East of the Tharsis rise can be seen the enormous near-equatorial gash that marks the canyon system Valles Marineris.
Valles Marineris is significantly larger than the Grand Canyon. While the Grand Canyon extends about 446 km (277 miles) in length, the Valles Marineris system spans more than 4,000 km (2,500 miles), covering approximately 20 percent of the circumference of Mars.123
In terms of depth, the central depression of Valles Marineris reaches up to 9 km (5.6 miles), which is about five times the depth of the Grand Canyon. Furthermore, while the Grand Canyon was primarily formed by erosion from the Colorado River, Valles Marineris was formed mainly by faulting, though it has been further enlarged by erosional processes.123