Casius Quadrangle - Concentric Crater Fill

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.

• 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.