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). Casius quadrangle contains part of Utopia Planitia and a small part of Terra Sabaea. 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). The quadrangle covers an approximate area of 4.9 million square km, or a little over 3% of Mars’ surface area.
Origin of name
Casius is the name of a telescopic albedo feature located at 40° N and 100° E on Mars. The feature was named by Schiaparelli in 1888 after Mt Casius in Egypt, famous in antiquity for the nearby coastal marshes in which whole armies were reputed to have drowned. The name was approved by the International Astronomical Union (IAU) in 1958.
Physiography and geology
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. Other features associated with ground ice are Scalloped Topography, Ring Mold Craters, and Concentric Crater Fill.
Polygonal patterned ground
Polygonal, patterned ground is quite common in some regions of Mars, especially in scalloped topography. It is commonly believed to be caused by the sublimation of ice from the ground. Sublimation is the direct change of solid ice to a gas. This is similar to what happens to dry ice on the Earth. Places on Mars that display polygonal ground may indicate where future colonists can find water ice. Patterned ground forms in a mantle layer that fell from the sky when the climate was different. Polygonal ground is generally divided into two kinds: high center and low center. The middle of a high center polygon is 10 meters across and its troughs are 2–3 meters wide. Low center polygons are 5–10 meters across and the boundary ridges are 3–4 meters wide. Low center polygons have been proposed as a marker for ground ice.
Ring mold craters
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." They may be an easy way for future colonists of Mars to find water ice.
Concentric crater fill
Concentric crater fill is when the floor of a crater is mostly covered with a large number of parallel ridges. They are thought to result from a glacial type of movement. 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. 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. The ice accumulated in the crater from snowfall in previous climates.
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.
Glaciers
Old glaciers are found in many places on Mars. Some are associated with gullies.
Nilosyrtis
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.