Gusev crater—A 60-km-wide impact crater (14.6°S, 175.5°E) in which the Mars Exploration Rover Spirit landed. The southern rim of the crater is breached by a large channel, Ma’Adim Vallis, thought to have formed by a large flood. A lake may have temporarily formed in the crater at the time of the flood, although Spirit found no evidence for such a lake.


Hecates Tholus—A 180-km-wide, 8-km-high volcano (32.1°N, 150.2°E) in Elysium with slopes densely dissected by narrow channels. The channels have been attributed to melting of snow by volcanic heat, possibly accompanied by hydrothermal circulation.


Hellas—A large, deep impact basin (40°S, 70°E) within the southern uplands that contains the lowest point on the planet (–9.2 km). The basin is one of the oldest topographic features of the planet, having formed deep within the era of heavy bombardment. If early Mars was warm and wet, as suggested by the widespread dissection of the oldest terrains, then Hellas would formerly have contained a large lake or sea.


Holden crater—A 140-km-diameter impact crater (27°S, 326°E) in the southern highlands. The crater has well-developed deltas on its floor at the ends of channels that breach the crater rim.


Meridiani Planum—An almost level plain (0°N, 355°E) on which the Mars Exploration Rover Opportunity landed in 2004. Beneath the plain is a kilometers-thick sequence of bedded sediments that appears to rest on an older, more cratered basement.


Nanedi Vallis—A large branching valley (5°N, 310°E) similar to Nirgal Vallis but located in Xanthe Terraat.


Nirgal Vallis—A large branching valley (28°S, 320°E) that is younger in age than typical branching valleys in the cratered uplands. Its characteristics suggest an origin by groundwater sapping rather than surface runoff. Gullies on its walls may indicate recent water-abetted slope failure.


Noachian uplands—Heavily cratered terrain that has survived from the era of heavy meteorite bombardment that ended around 3.7 billion years ago. The surface is heavily dissected by branch valley networks, which suggest warmer climatic conditions when the terrain formed. The rocks of Columbia Hills may be representative of what composes the terrain.


Olympus Mons—Roughly three times taller than Mount Everest, Olympus Mons (17°N, 225°E) is the tallest known volcano in the solar system. It probably grew slowly over almost the entire life of the planet by massive eruptions of basaltic lava widely spaced in time.


Tharsis—A volcanic province, roughly 3,500 km across, centered on the equator at 250°E, and containing some of the largest volcanos in the solar system. The province has been a center of volcanism for almost the entire history of the planet. The massive volcanic pile was already in place at the end of heavy bombardment 3.7 billion years ago, and activity has continued ever since.


Valles Marineris—A vast system of interconnected canyons more than 4,000 km long, and up to 600 km wide and 10 km deep. The canyons formed by faulting but have been substantially modified by other processes such as water erosion and mass-wasting. They contain thick sequences of sulfate-rich sediments. The canyon may have formerly contained lakes that drained catastrophically to the east.



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