26 May 2005

This picture is a mosaic of two Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images of sedimentary rock outcrops in Aram Chaos, near Ares Vallis, Mars. Aram Chaos is an impact crater that was nearly completely filled with material, some of which is light-toned, layered, sedimentary rock. The MGS Thermal Emission Spectrometer team detected crystalline hematite in Aram Chaos, attesting to its potential similarity to some of the rocks in Meridiani Planum, where the Mars Exploration Rover (MER-B), Opportunity, has been operating. During April 2005, an opportunity arose to acquire a MOC narrow angle camera image that would mosaic with a previous picture, R11-02268. The figure shown here is a mosaic of that earlier image, obtained in November 2003, and the newer picture, from April 2005. Sunlight illuminates the scene from the right, and north is toward the bottom. A steep slope is seen near the top of the image. It formed in light-toned sedimentary rock, and it has shed debris to form a suite of darker-toned talus deposits. These deposits are the products of dry mass movement; the darker tone of the debris might be an indication that the material is less weathered or coarse-grained. Evident below the scarp are several light-toned yardangs, sculpted by wind. Erosion of the yardang-forming material, interpreted to be sedimentary rock, has revealed dark-toned blocks, separated by troughs. The blocks pre-date the deposition of the yardang-forming material. The presence of these broken-up blocks suggests that a chaotic terrain pattern formed in Aram Chaos long ago, before subsequent deposition of material that later became the light-toned, sedimentary rock. The geologic history recorded in Aram Chaos is no less complex than has been observed by MOC in other large craters, such as Gale.