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Mojave is an impact crater in the Oxia Palus quadrangle of Mars located at 7.5° N and 33.0° W. It is 58 km in diameter. It was named after a town in California, USA. Located in the Xanthe Terra region, Mojave has alluvial fans that look remarkably similar to landforms in the Mojave Desert in the American southwest. Fans inside and around the outsides of the crater are closely similar to Earth's alluvial fans. As on Earth, the largest rocks are near the mouths of the fans. Because the channels start at ridge tops, it is believed they were formed by heavy downpours. Researchers have suggested that the rain may have been initiated by impacts.〔http://hirise.lpl.arizona.edu/PSP_001415_1875〕〔http://www.uahirise.org/ESP_038851_1900〕 Some parts of the crater display a high concentration of closely spaced pits. Pits show little or no evidence of rims or ejecta. The pits are so close to each other that adjacent pits often share the same wall. It is believed that the pits form from steam produced when the heat from the impact process interacts with ice in the ground.〔Boyce, J. et al. 2012. Origin of small pits in Martian impact craters. Icarus: 221, 262-275.〕〔Tornabene, L., et al. 2012. Widspread crater-related pitted materials on Mars: Further evidence for the role of target volatiles during the impact process. Icarus: 220, 348-368.〕 Many craters once contained lakes.〔Cabrol, N. and E. Grin. 2001. The Evolution of Lacustrine Environments on Mars: Is Mars Only Hydrologically Dormant? Icarus: 149, 291-328.〕〔Fassett, C. and J. Head. 2008. Open-basin lakes on Mars: Distribution and implications for Noachian surface and subsurface hydrology. Icarus: 198, 37-56.〕〔Fassett, C. and J. Head. 2008. Open-basin lakes on Mars: Implications of valley network lakes for the nature of Noachian hydrology.〕 Because some crater floors show deltas, we know that water had to be present for some time. Dozens of deltas have been spotted on Mars.〔Wilson, J. A. Grant and A. Howard. 2013. Inventory of Equatorial Alluvial Fans and Deltas on Mars. 44th Lunar and Planetary Science Conference.〕 Deltas form when sediment is washed in from a stream entering a quiet body of water. It takes a bit of time to form a delta, so the presence of a delta is exciting; it means water was there for a time, maybe for many years. Primitive organisms may have developed in such lakes; hence, some craters may be prime targets for the search for evidence of life on the Red Planet.〔Newsom H. , Hagerty J., Thorsos I. 2001. Location and sampling of aqueous and hydrothermal deposits in martian impact craters. Astrobiology: 1, 71-88.〕 The depth of Mojave is approximately 2,600 meters (1.63 miles). Based on its ratio of depth to diameter, researchers believe it is very young. It is not old enough to have accumulated much material and start to fill. Its relatively undegraded state helps scientists model impact processes on Mars.〔http://hirise.lpl.arizona.edu/dtm/dtm.php?ID=PSP_00481_1875〕 If one measures the diameter of a crater, the original depth can be estimated with various ratios. Because of this relationship, researchers have found that many Martian craters contain a great deal of material; much of it is believed to be ice deposited when the climate was different.〔Garvin, J., et al. 2002. Global geometric properities of martian impact craters. Lunar Planet Sci. 33. Abstract @1255.〕 Mojave is a rayed crater, another indication of its youth, and is the largest such crater on Mars. Based on crater counts of its ejecta blanket, it is thought to be about 3 million years old. It is believed to be the most recent crater of its size on Mars, and has been identified as the probable source of the shergottite meteorites collected on Earth. However, the latter hypothesis is controversial. Image:Wikimojave.jpg|Mojave Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Image:Alluvial Fans in Mojave Crater.jpg|Alluvial fans in Mojave, as seen by HiRISE. The crater rim is on the right. A branched network of channels runs downward towards the left. Image:Mojave Crater.jpg|Another view of Mojave from HiRISE. North is at bottom. ==See also== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mojave (crater)」の詳細全文を読む スポンサード リンク
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