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Arcadia Planitia is a smooth plain with fresh lava flows and Amazonian volcanic flows on Mars. It was named by Giovanni Schiaparelli in 1882 after the Arcadia region of ancient Greece. It dates from the Amazonian period's Arcadia formation's lava flows and small cinder cones. It includes a more recently developed large region of aeolian materials derived from periglacial processes. It is located northwest of the Tharsis region in the northern lowlands, spanning the region 40-60° North and 150-180° West in the Cebrenia quadrangle and centered at . Part of it is in the Diacria quadrangle. Arcadia marks a transition from the thinly cratered terrain to its north and the very old cratered terrain to the south. On its east it runs into the Alba Mons volcanoes. Its elevation relative to the geodetic datum varies between 0 and -3 km. 〔R. Greeley, ("Arcadia Planitia" ) URL accessed July 31, 2006.〕 In a lot of the low areas of Arcadia, one finds grooves and sub-parallel ridges. These indicate movement of near surface materials and are similar to features on earth where near surface materials flow together very slowly as helped by the freezing and thawing of water located between ground layers. This supports the proposition of ground ice in the near surface of Mars in this area. This area represents an area of interest for scientists to investigate further. A website for Linux was also named after this, JCM Arcadia Planitia.〔http://arcadiaplanitia.jameschristianmartin.com〕 Wikimolaamazonisarcadia.jpg|MOLA map showing boundaries for part of Arcadia Planitia and other regions ==Gullies== Martian gullies are small, incised networks of narrow channels and their associated downslope sediment deposits, found on the planet of Mars. They are named for their resemblance to terrestrial gullies. First discovered on images from Mars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a single thread of incised ''channel'' linking the two, giving the whole gully an hourglass shape.〔Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.〕 They are believed to be relatively young because they have few, if any craters. A subclass of gullies is also found cut into the faces of sand dunes which themselves considered to be quite young. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research. The pictures below show gullies in Arcadia Planitia. Image:26420gullieswide.jpg|Wide view of group of gullies, as seen by HiRISE under HiWish program. Note that part of this image is enlarged in the following image. Image:26420gulliesclose.jpg|Close-up of gullies, as seen by HiRISE under HiWish program. Arrow points to streamlined features. This enlarged view shows an excellent view of polygons which are common where ice-rich ground freezes and thaws. 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「Arcadia Planitia」の詳細全文を読む スポンサード リンク
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