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Lobate debris aprons (LDAs) are geological features on Mars, first seen by the Viking Orbiters, consisting of piles of rock debris below cliffs.〔Carr, M. 2006. The Surface of Mars. Cambridge University Press. ISBN 978-0-521-87201-0〕〔Squyres, S. 1978. Martian fretted terrain: Flow of erosional debrid. Icarus: 34. 600-613.〕 These features have a convex topography and a gentle slope from cliffs or escarpments, which suggest flow away from the steep source cliff. In addition, lobate debris aprons can show surface lineations as do rock glaciers on the Earth.〔ISBN 0-8165-1257-4〕 Wikictxp13clifflda.jpg|Wide view of mesa with CTX showing Cliff face and location of Lobate Debris Apron (LDA) Location is Ismenius Lacus quadrangle. Wikifretesp 028313 2220cliff.jpg|Enlargement of previous CTX image of mesa This image shows the cliff face and detail in the LDA. Image taken with HiRISE under HiWish program. Location is Ismenius Lacus quadrangle. Wikildaf03 036777 2287.jpg|Lobate Debris Aprons (LDA's) around a mesa, as seen by CTX Mesa and LDA's are labeled so one can see their relationship. Radar studies have determined that LDA's contain ice; therefore these can be important for future colonists of Mars. Location is Ismenius Lacus quadrangle. WikiESP 036777 2290lda.jpg|Close up of Lobate debris apron (LDA), as seen by HiRISE under HiWish program Image:Lobate Debris Apron in Phlegra Montes.JPG|Lobate debris apron in Phlegra Montes, as seen by HiRISE. The debris apron is probably mostly ice with a thin covering of rock debris, so it could be a useful source of water. Scale bar is 500 meters long. Image:Lobate Debris Apron closeup.jpg|Close-up of surface of a lobate debris apron in Hellas quadrangle. Note the lines that are common in rock glaciers on the Earth. Image:Wide view of Debris Apron.jpg|View of a lobate debris apron along a slope in Arcadia quadrangle. Image:Face of Lobate Debris Apron.jpg|Place where a lobate debris apron begins. Note stripes which indicates movement. Image located in Ismenius Lacus quadrangle. The Mars Reconnaissance Orbiter's Shallow Radar gave a strong reflection from the top and base of LDAs, meaning that pure water ice made up the bulk of the formation (between the two reflections).〔http://www.planetary.brown.edu/pdfs/3733.pdf〕 This is evidence that the LDAs in Hellas Planitia are glaciers covered with a thin layer of rocks.〔Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350〕〔http://www.marstoday.com/news/viewpr.html?pid=18050〕〔http://news.brown.edu/pressreleases/2008/04/martian-glaciers〕〔Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf〕〔Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf〕 The experiments of the Phoenix lander and the studies of the Mars Odyssey from orbit show that frozen water exists just under the surface of Mars in the far north and south (high latitudes). Most of the ice was deposited as snow when the climate was different.〔Madeleine, J. et al. 2007. Exploring the northern mid-latitude glaciation with a general circulation model. In: Seventh International Conference on Mars. Abstract 3096.〕 The discovery of water ice in LDAs demonstrates that water is found at even lower latitudes. Future colonists on Mars will be able to tap into these ice deposits, instead of having to travel to much higher latitudes. Another major advantage of LDAs over other sources of Martian water is that they can easily be detected and mapped from orbit. Lobate debris aprons are shown below from the Phlegra Montes which are at a latitude of 38.2 degrees north. The Phoenix lander set down at about 68 degrees north latitude, so the discovery of water ice in LDAs greatly expands the range of water easily available on Mars.〔http://www.planetary.org/explore/topics/phoenix〕 It is far easier to land a spaceship near the equator of Mars, so the closer water is available to the equator the better it will be for colonists. == Lineated floor deposits == The floors of some channels show ridges and grooves that seem to flow around obstacles; these features are called lineated floor deposits or lineated valley fill (LVF). Like lobate debris aprons, they are believed to be ice-rich. Some glaciers on the Earth show such features. It has been suggested that lineated floor deposits began as LDAs.〔Sourness, C., B. Hubbard, R. Milliken, D. Quincey. 2012. An inventory and population-scale analysis of martian glacier-like forms. Icarus 217, 243-255.〕〔Souness, C. and B. Hubbard. 2013. An alternative interpretation of late Amazonian ice flow: Protonilus Mensae, Mars. Icarus 225, 495-505.〕 By tracing the paths of the curved ridges characteristic of LDAs, researchers have come to believe that they straighten out to form the ridges of LVF. Both lineated floor deposits and lobate debris aprons often display a strange surface formation called brain terrain because it looks like the surface of the human brain. Wikifrettedctxp22.jpg|Wide CTX view showing mesa and buttes with Lobate debris aprons and lineated valley fill around them. Location is Ismenius Lacus quadrangle. WikiESP 020769 2225fretted.jpg|Close-up of Lineated Valley Fill (LVF), as seen by HiRISE under HiWish program Note: this is an enlargement of the previous CTX image. Wikifrettedctxpo5.jpg|Wide CTX view of mesa showing Lineated Valley Fill and Lobate Debris Apron (LDA). Both are believed to be debris covered glaciers. Location is Ismenius Lacus quadrangle. Wikifretesp 027639 2210lda.jpg|Close-up of Lobate Debris Apron from the previous CTX image of a mesa. Image shows open-cell brain terrain and closed-cell brain terrain which is more common. Open-cell brain terrain is thought to hold a core of ice. Image is from HiRISE under HiWish program. File:25246brainseroding.jpg|Closed-cell brain terrain, as seen by HiRISE under the HiWish program. This type of surface is common on lobate debris aprons, concentric crater fill, and lineated valley fill. File:Htalk23815 2215lvfclose.jpg|Open and closed-cell brain terrain, as seen by HiRISE, under HiWish program. Reull Vallis, pictured below, displays these deposits.〔http://themis.asu.edu/zoom-20021022a〕 Sometimes the lineated floor deposits show a chevron pattern which is further evidence of movement. The picture below taken with HiRISE of Reull Vallis shows these patterns. 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「Lobate debris apron」の詳細全文を読む スポンサード リンク
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