 Peace Vallis and relatedalluvial fan near theCuriosity rover landing ellipse and landing site (Bradbury Landing) (noted by cross [+]). | |
| Coordinates | 4°13′S137°14′E / 4.21°S 137.23°E /-4.21; 137.23 |
|---|---|
| Length | 35.24 km (21.90 mi) |
| Naming | Adopted by theIAU on September 26, 2012, after the Peace River in British Columbia and Alberta, Canada.[1] |
Peace Vallis is an ancient stream valley on the northern rim ofGale Crater on the planetMars. It is notable for its associatedalluvial fan which lies near the Mars Science LaboratoryCuriosity landing site (Bradbury Landing). The valley and alluvial fan provide evidence for geologically recent (Amazonian-aged)fluvial activity[2][3] and sustained water flow[4] on Mars. Recent high-resolution orbital images of Peace Vallis and itswatershed also suggest that at least one glacial episode affected Gale crater.[5] All of this evidence has implications for the history ofwater on Mars and the planet's long-termhabitability.[6] Understanding Peace Vallis and its fan also provides geologic context for the rocks observed on the ground by theCuriosity rover.[7]
The valley is centered at4°13′S137°14′E / 4.21°S 137.23°E /-4.21; 137.23[1] in the northeasternAeolis quadrangle of Mars and drains approximately 1,500 square kilometers (580 sq mi) of the northern rim of Gale Crater.[8] While the stream was active, surface water and groundwater drained to the south into a low-lying plain in the northern interior of the crater (Aeolis Palus) where the stream valleydebouched into a large alluvial fan (Peace Vallis fan).
Gale Crater itself is a 154-kilometer (96 mi)-diameter impact crater that straddles the martian hemisphericdichotomy between the heavily cratered southern highlands and the lower elevation plains (Elysium Planitia) to the north. Gale Crater is noteworthy for its enigmatic 5-kilometer (3.1 mi)-high crescent-shaped central mound,Aeolis Mons (known informally as Mt. Sharp). The crater is lateNoachian or EarlyHesperian in age (approximately 3.65 to 3.55 billion years old).[9]
The northern rim of Gale Crater is heavily eroded and hosts a number of geomorphic features indicating the effects of flowing water. These include valleys, gullies, and canyons; sinuous ridges interpreted to beinverted channels; and alluvial fan-like mesas.[10] Peace Vallis and its alluvial fan is the largest and best studied of these fluvial features in northern Gale Crater.
Peace Vallis is named after the Peace River in Alberta and British Columbia, Canada. The name was adopted by theInternational Astronomical Union (IAU) on September 26, 2012.Vallis is the Latin word for valley.[1]
Peace Vallis is avalley network characterized by a branching (dendritic) pattern of tributary valleys that resembles river drainage basins on Earth. They are common on the older heavily cratered regions of Mars. Most planetary scientists agree that valley networks were formed by flowing water, but the source of the water is still debated.[11] Some argue that rainfall on a warm and wet early mars produced them.[12] Others have suggested they were produced bymass wasting,[13]spring sapping,[14] or fromsnowmelt[15] on an ancient Mars whose climate was dry and cold much like today's.
The Peace Vallisdrainage basin (or catchment) covers an area of about 1,500 km2 (579 mi2). This area sits 1,300 m (4,265 ft)[5] above the crater floor and consists of gently sloping plains interspersed with hills roughly 100 to 350 m (328 to 1,148 ft) high. These irregular hills are mostly mantled with debris that appear to be some combination ofaeolian deposits andcolluvium.[16] Erosion of the watershed surface has produced a mottled scoured appearance, suggesting mobilization and transport of sediments into topographic lows.
Compared with most terrestrial valleys carved by rainfall, thedrainage density (stream length per unit area) of Peace Vallis and its tributaries is very low. There is a lack of highly integrated fluvial channels,[17] and the areas between the tributary valleys (interfluves) are undissected by smaller valleys or gullies. The drainage density of the Peace Vallis system has been estimated to be 0.15 km–1.[16] In contrast, drainage densities of rivers on Earth range from 2 to 30 km–1.[18] Factors that control drainage density include slope, rock type (which determinesinfiltration capacity)[19] and climate (mainly precipitation). The low drainage density of Peace Vallis suggests an environment of relatively gentle slopes, very low (or infrequent) precipitation, permeable soils orbedrock, or some combination of the three.[20]
The valleys are U-shaped intopographic profile, with widths ranging from 80 to 900 meters (262 to 2,950 feet) and a mean of 300 meters (984 feet). The main or trunk valley is about 32 km (20 miles) long.[16]
Curiosity rover landed near the end of the Peace Vallis fan. Peace Vallis fan covers 80 km2 (31 sq mi) and obtained water from an area of 730 km2 (280 sq mi). Peace Vallis enters Gale Crater through a 15 km-wide (9.3 mi) gap in its rim. Calculations suggest that the fan has an average thickness of 9 m (30 ft). Numerous inverted channels are visible on the western surface of the fan. Runoff through Peace Vallis that made the fan is estimated to be between 600 and 6,000 m (0.37 and 3.73 mi); therefore a hydrologic cycle probably lasted at least thousands of years. The water that flowed in Peace Vallis is believed to be from precipitation, possibly in the form of snow.[16]
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