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The Phaethontis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Phaethontis quadrangle is also referred to as MC-24 (Mars Chart-24). The Phaethontis quadrangle lies between 30° and 65 ° south latitude and 120° and 180 ° west longitude on Mars. This latitude range is where numerous gullies have been discovered. An old feature in this area, called Terra Sirenum lies in this quadrangle; Mars Reconnaissance Orbiter discovered iron/magnesium smectites there. Part of this quadrangle contains what is called the Electris deposits, a deposit that is 100–200 meters thick. It is light-toned and appears to be weak because of few boulders. Among a group of large craters is Mariner Crater, first observed by the Mariner IV spacecraft in the summer of 1965. It was named after that spacecraft. A low area in Terra Sirenum is believed to have once held a lake that eventually drained through Ma'adim Vallis. Russia's Mars 3 probe landed in the Phaethontis quadrangle at 44.9° S and 160.1° W in December 1971. It landed at a speed of 75 km per hour, but survived to radio back 20 seconds of signal, then it went dead. Its message just appeared as a blank screen. ==Martian Gullies== (詳細はGorgonum Chaos〔http://hirise.lpl.arizona.edu/PSP_004071_1425〕〔http://hirise.lpl.arizona.edu/PSP_001948_1425〕 and in many craters near the large craters Copernicus and Newton (Martian crater).〔http://hirise.lpl.arizona.edu/PSP_004163_1375〕〔U.S. department of the Interior U.S. Geological Survey, Topographic Map of the Eastern Region of Mars M 15M 0/270 2AT, 1991〕 Gullies occur on steep slopes, especially on the walls of craters. Gullies are believed to be relatively young because they have few, if any craters. Moreover, they lie on top of sand dunes which themselves are considered to be quite young. Usually, each gully has an alcove, channel, and apron. Some studies have found that gullies occur on slopes that face all directions, others have found that the greater number of gullies are found on poleward facing slopes, especially from 30-44 S. Although many ideas have been put forward to explain them,〔http://www.psrd.hawaii.edu/Aug03/MartianGullies.html〕 the most popular involve liquid water coming from an aquifer, from melting at the base of old glaciers, or from the melting of ice in the ground when the climate was warmer.〔Forget, F. et al. 2006. Planet Mars Story of Another World. Praxis Publishing. Chichester, UK.〕 Because of the good possibility that liquid water was involved with their formation and that they could be very young, scientists are excited. Maybe the gullies are where we should go to find life. There is evidence for all three theories. Most of the gully alcove heads occur at the same level, just as one would expect of an aquifer. Various measurements and calculations show that liquid water could exist in aquifers at the usual depths where gullies begin.〔 One variation of this model is that rising hot magma could have melted ice in the ground and caused water to flow in aquifers. Aquifers are layer that allow water to flow. They may consist of porous sandstone. The aquifer layer would be perched on top of another layer that prevents water from going down (in geological terms it would be called impermeable). Because water in an aquifer is prevented from going down, the only direction the trapped water can flow is horizontally. Eventually, water could flow out onto the surface when the aquifer reaches a break—like a crater wall. The resulting flow of water could erode the wall to create gullies.〔http://www.space.com/scienceastronomy/mars_aquifer_041112.html〕 Aquifers are quite common on Earth. A good example is "Weeping Rock" in Zion National Park Utah.〔Harris, A and E. Tuttle. 1990. Geology of National Parks. Kendall/Hunt Publishing Company. Dubuque, Iowa〕 As for the next theory, much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust. This ice-rich mantle, a few yards thick, smoothes the land, but in places it has a bumpy texture, resembling the surface of a basketball. The mantle may be like a glacier and under certain conditions the ice that is mixed in the mantle could melt and flow down the slopes and make gullies.〔http://www.msnbc.msn.com/id/15702457?〕 Because there are few craters on this mantle, the mantle is relatively young. An excellent view of this mantle is shown below in the picture of the Ptolemaeus Crater Rim, as seen by HiRISE. The ice-rich mantle may be the result of climate changes.〔http://news.nationalgeographic.com/news/2008/03/080319-mars-gullies_2.html〕 Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water comes back to ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor will condense on the particles, then fall down to the ground due to the additional weight of the water coating. When Mars is at its greatest tilt or obliquity, up to 2 cm of ice could be removed from the summer ice cap and deposited at midlatitudes. This movement of water could last for several thousand years and create a snow layer of up to around 10 meters thick. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulating the remaining ice. Measurements of altitudes and slopes of gullies support the idea that snowpacks or glaciers are associated with gullies. Steeper slopes have more shade which would preserve snow.〔 Higher elevations have far fewer gullies because ice would tend to sublimate more in the thin air of the higher altitude. The third theory might be possible since climate changes may be enough to simply allow ice in the ground to melt and thus form the gullies. During a warmer climate, the first few meters of ground could thaw and produce a "debris flow" similar to those on the dry and cold Greenland east coast. Since the gullies occur on steep slopes only a small decrease of the shear strength of the soil particles is needed to begin the flow. Small amounts of liquid water from melted ground ice could be enough.〔http://www.spaceref.com:16090/news/viewpr.html?pid=7124,〕 Calculations show that a third of a mm of runoff can be produced each day for 50 days of each Martian year, even under current conditions. Image:Electris Depsoit.jpg|Electris Deposit, as seen by HiRISE. Electris deposit is light-toned and smooth in the image in contrast to rough materials below. Location is Phaethontis quadrangle. Image:Electris Deposit Layers.jpg|Layers in light-toned Electris Deposit, as seen by HiRISE on the Mars Reconnaissance Orbiter. Gullies are visible on the left. Image:Gorgonum in Phaethontis.JPG|Gorgonum Chaos as seen by Mars Reconnaissance Orbiter HiRISE. Image about 4 km wide. Image:Gully in Phaethontis.jpg|Group of gullies on north wall of crater that lies west of the crater Newton (41.3047 degrees south latitude, 192.89 east longitide). Image taken with Mars Global Surveyor under the MOC Public Targeting Program. Image:Crater wall inside Mariner Crater.JPG|Crater wall inside Mariner Crater showing a large group of gullies, as seen by HiRISE. Image:Ptolemaeus Crater Rim.JPG|Ptolemaeus Crater Rim, as seen by HiRISE. Click on image to see excellent view of mantle deposit. Image:Close up view of gullies.jpg|Gullies. Notice how channels curve around obstacles, as seen by HiRISE. Image:Branched gullies.jpg|Gullies with branches, as seen by HiRISE. Image:Deep Gullies.jpg|Group of deep gullies, as seen by HiRISE. Image:Wide view of gully on hill.JPG|CTX image of the next image showing a wide view of the area. Since the hill is isolated it would be difficult for an aquifer to develop. Rectangle shows the approximate location of the next image. Image:Gully on mound.JPG|Gully on mound as seen by Mars Global Surveyor, under the MOC Public Targeting Program. Images of gullies on isolated peaks, like this one, are difficult to explain with the theory of water coming from aquifers because aquifers need large collecting areas. Image:28386myglaciers.jpg|Another view of the previous gully on a mound. This one is with HiRISE, under the HiWish program. This view shows most of the apron and two old glaciers associated with it. All that is left of the glaciers are terminal moraines. Image:Context image for gullies in crater and trough.JPG|MOLA context image for the series of three images to follow of gullies in a trough and nearby crater. Image:Gullies in trough and crater.jpg|Gullies in a trough and nearby crater, as seen by HiRISE under the HiWish program. Scale bar is 500 meters long. Image:Gullies in crater under HiWish.JPG|Close-up of gullies in crater, as seen by HiRISE under the HiWish program. Image:Gullies in trough.JPG|Close-up of gullies in trough, as seen by HiRISE under the HiWish program. These are some of the smaller gullies visible on Mars. Image:ESP_020012gulliescropped.jpg|Gullies near Newton Crater, as seen by HiRISE, under the HiWish program. Place where there was an old glacier is labeled. Image:20803 gullies.jpg|HiRISE image, taken under HiWish program, of gullies in a crater in Terra Sirenum. Image:20803gullies with glacier remains.jpg|Gullies with remains of a former glacier in crater in Terra Sirenum, as seen by HiRISE under HiWish program. Image:Gullies near Newton Crater.jpg|Gullies near Newton Crater, as seen by HiRISE under the HiWish Program. Image:Gullies in Terra Sirenum.jpg|Gullies in a crater in Terra Sirenum, as seen by HiRISE under the HiWish Program. Image:21845gulliespatt.jpg|Close-up of gully showing multiple channels and patterned ground, as seen by HiRISE under the HiWish program. Wikigasa.jpg|Gasa Crater, as seen by CTX Note: Gasa Crater is the smaller crater. It is believed the impact that created Gasa occurred in a debris-covered glacier. WikigasaESP 027663 1440.jpg|Gullies in Gasa Crater, as seen by HiRISE. ESP 039753 1385gulliespits.jpg|Gullies in crater in Phaethontis quadrangle, as seen by HiRISE under HiWish program ESP 039621 1315gullies2levels.jpg|Gullies in two levels of a crater wall, as seen by HiRISE under HiWish program. Gullies at two levels suggests they were not made with an aquifer, as was first suggested. Location is Phaethontis quadrangle. ESP 039621 1315gullies.jpg|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program. Location is Phaethontis quadrangle. ESP 039621 1315aprons.jpg|Close-up of gully aprons showing they are free of craters; hence very young. Location is Phaethontis quadrangle. Picture was taken by HiRISE under HiWish program. ESP 039793 1385gullies.jpg|Gullies in crater, as seen by HiRISE under HiWish program. Location is Phaethontis quadrangle. ESP 039793 1385channeldetails.jpg|Close up of gullies in crater showing channels within larger valleys and curves in channels. These characteristics suggest they were made by flowing water. Note: this is an enlargement of the previous image by HiRISE under HiWish program. Location is Phaethontis quadrangle. ESP 039793 1385channelsclose.jpg|Close up of gully network showing branched channels and curves; these characteristics suggest creation by a fluid. Note: this is an enlargement of a previous wide view of gullies in a crater, as seen by HiRISE under HiWish program. Location is Phaethontis quadrangle. 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「Phaethontis quadrangle」の詳細全文を読む スポンサード リンク
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