(Released 8 July 2002)
This THEMIS visible image shows several "fretted" channels within Deuteronilus Mensae in the northern plains of Mars. These linear troughs appear to have been extensively modified by surficial processes. Their floors contain knobby or "scabby" materials that have been modified to produce a pitted, knobby surface. This type of surface is common in the northern highlands of Mars, and its location and pitted texture has been suggested to indicate that these materials once contained ice that has since been removed to form the pits (devolatization). Many of the sloping surfaces in this region image have unusual deposits of material that occur preferentially on the cold, north-facing slopes. These deposits are seen frequently at mid-northern and southern latitudes, and have a distinct, rounded boundary that typically occurs at approximately the same distance below the ridge crest. It has been suggested that these deposits once draped the entire surface and have since been removed from all but the north-facing slopes. In some regions these deposits have ridges that parallel the cliff, suggestive of downslope movement and compression, possibly aided by ice. In some areas these slope deposits are darker than the material on the floor of the channel, and appear to sit on top of the pitted channel-floor materials. This relationship indicates that the slope materials have slightly different properties, leading to their darker tone, and are younger (and thus on top of) the channel floors. The presence of water ice in the surface in this area is a likely possibility to account for many of the features observed. This ice may still be present near the surface and this region may still be undergoing modification today.