MGS MOC Release No. MOC2-487, 18 September 2003

This June 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows patterns created by defrosting processes on the south polar seasonal ice cap. Seasonal cap refers to the part of the polar cap that comes and goes with the seasons, as opposed to the residual cap, which lasts throughout the summer. The area shown here, in summer, will have no frost. This picture was taken during southern spring. As the seasonal frost begins to sublime away, dark cracks form a polygon pattern, and wind blows material to form varied bright and dark streaks. What is unknown is whether the dark streaks consist of sand and silt from beneath the seasonal frost, or whether they, too, consist of frost that has been transformed into coarse-grained particles that can be mobilized by wind. Alternatively, the streaks represent erosion and removal of frost, rather than deposition of granular material. The bright streaks are most likely made of frost--whether they are water ice or carbon dioxide ice remains to be determined. The bulk of the frosted surface shown here is carbon dioxide ice. The image is located near 87.3°S, 192.4°W. The picture covers an area 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.