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The Casius quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the north central portion of Mars’ eastern hemisphere and covers 60° to 120° east longitude (240° to 300° west longitude) and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Casius quadrangle is also referred to as MC-6 (Mars Chart-6).[1] The southern and northern borders of the Casius quadrangle are approximately 3,065 km and 1,500 km wide, respectively. The north to south distance is about 2,050 km (slightly less than the length of Greenland).[2] The quadrangle covers an approximate area of 4.9 million square km, or a little over 3% of Mars’ surface area.[3]
Casius is the name of a telescopic albedo feature located at 40° N and 100° E on Mars. The feature was named for the Latin epithet for Zeus from his sanctuaries in Egypt and Syria. The name was approved by the International Astronomical Union (IAU) in 1958.[4]
The high latitude Casius quadrangle bears several features that are believed to indicate the presence of ground ice. Patterned ground is one such feature. Usually, polygonal shapes are found poleward of 55 degrees latitude.[5] Other features associated with ground ice are Scalloped Topography,[6] Ring Mold Craters, and Concentric Crater Fill.
Map of Casius quadrangle with major features labeled.
Patterned ground in the form of polygonal features is associated with ground ice. It is rare to be found this far south (45 degrees north latitude). Picture taken by Mars Global Surveyor.
Periglacial Forms in Utopia, as seen by HiRISE. Click on image to see patterned ground and Scalloped Topography.
Nilosyrtis runs from about 280 to 304 degrees west longitude, so like several other features, it sits in more than one quadrangle. Part of Nilosyrtis is in the Ismenius Lacus quadrangle, the rest is in Casius quadrangle.
Channel in Nilosyrtis that was formed when a lake in a 45-mile-wide crater drained, as seen by THEMIS.
Landing Site in Nilosyrtis, as seen by THEMIS. Site is flat and contains water-altered clay minerals.
Nilosyrtis, as seen by HiRISE. Click on image to see layers.
Ring Mold Craters look like the ring molds used in baking. They are believed to be caused by an impact into ice. The ice is covered by a layer of debris. They are found in parts of Mars that have buried ice. Laboratory experiments confirm that impacts into ice result in a "ring mold shape."[7][8][9] They may be an easy way for future colonists of Mars to find water ice.
CTX context image for next image taken with HiRISE. Box indicates image footprint of following image.
Possible ring mold crater, as seen by HiRISE under the HiWish program. Crater shape is due to impact into ice.
Ring-mold craters form when an impact goes through to an ice layer. The rebound forms the ring-mold shape, and then dust and debris settle on the top to insulate the ice.
Concentric crater fill is when the floor of a crater is mostly covered with a large number of parallel ridges.[10] They are thought to result from a glacial type of movement.[11][12] Sometimes boulders are found on concentric crater fill; it is believed they fell off crater wall, and then were transported away from the wall with the movement of the glacier.[13][14]Erratics on Earth were carried by similar means. Based on accurate topography measures of height at different points in these craters and calculations of how deep the craters should be based on their diameters, it is thought that the craters are 80% filled with mostly ice. That is, they hold hundreds of meters of material that probably consists of ice with a few tens of meters of surface debris.[15] The ice accumulated in the crater from snowfall in previous climates.[16]
High resolution pictures taken with HiRISE reveal that some of the surfaces of concentric crater fill are covered with strange patterns called closed-cell and open-cell brain terrain. The terrain resembles a human brain. It is believed to be caused by cracks in the surface accumulating dust and other debris, together with ice sublimating from some of the surfaces.[17]
Wide-view of concentric crater fill, as seen by HiRISE.
Concentric Crater Fill Close-up of near the top of previous image, as seen by HiRISE. The surface debris covers water ice.
Well-developed hollows of concentric crater fill, as seen by HiRISE under the HiWish program.
Close-up that shows cracks containing pits on the floor of a crater containing concentric crater fill, as seen by HiRISE under HiWish program.
Close-up that shows cracks containing pits on the floor of a crater, as seen by HiRISE under HiWish program. Cracks may start as a line of pits that enlarge, then join.
Many features on Mars, including many in Casius quadrangle, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degrees[18][19] Large changes in the tilt explains many ice-rich features on Mars.
Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles.[20] Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure. This increased pressure allows more dust to be held in the atmosphere. Moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes.[21][22] General circulation models of the Martian atmosphere predict accumulations of ice-rich dust in the same areas where ice-rich features are found.[23] When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust.[24][25][26] The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind.[27] Note, that the smooth surface mantle layer probably represents only relative recent material.
Nilosyrtis is one of the sites proposed as a landing site for the Mars Science Laboratory. However, it did not make the final cut. It was in the top 7, but not in the top 4. The aim of the Mars Science Laboratory is to search for signs of ancient life. It is hoped that a later mission could then return samples from sites identified as probably containing remains of life. To safely bring the craft down, a 12-mile-wide, smooth, flat circle is needed. Geologists hope to examine places where water once ponded.[28] They would like to examine sediment layers.
Crater in the Adamas Labyrinthus Region, as seen by HiRISE. The original image shows many interesting details.
Bacolor Crater Ejecta, as seen by HiRISE. Scale bar is 1000 meters long.
Astapus Colles Mounds and Knobs, as seen by HiRISE. Scale bar is 500 meters long.
Surface of Nilosyrtis Mensae showing ridges and cracks, as seen by HiRISE, under the HiWish program.
Another view of surface of Nilosyrtis Mensae, as seen by HiRISE, under the HiWish program.
CTX image showing area in next image.
Layers in craters, as seen by HiRISE under the HiWish program. Area was probably covered over by these layers; the layers have now eroded away except for the protected interior of craters.
Layers, as seen by HiRISE under HiWish program.
Layers in Monument Valley. These are accepted as being formed, at least in part, by water deposition. Since Mars contains similar layers, water remains as a major cause of layering on Mars.
Dikes as seen by HiRISE under the HiWish program.
Pits that seem to be forming cracks, as seen by HiRISE under HiWish program.
Holes and hollows on crater floor, as seen by HiRISE under HiWIsh program.
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