10 January 2004
While it is summer in Gusev Crater, where the Mars Exploration Rover, Spirit, is operating, it is winter in the martian northern hemisphere. Just this week, the north polar dune fields began to emerge into sunlight after months of frigid darkness. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) view of frost-covered north polar dunes was acquired on 8 January 2004. The steepest slopes on the dunes--their slipfaces--point toward the upper right (northeast), indicating that the dominant winds responsible for their formation came from the opposite direction (lower left, southwest). Sunlight illuminates these dunes from the lower left, which may seem surprising because the brightest slopes on the dunes face the lower right. The brighter slopes are a frost phenomenon; most likely, these are areas with thicker frost deposits. In summer, the dunes would not have frost and would appear much darker than their surroundings. This early view of north polar dunes in winter is located near 75.8°N, 266.3°W. This view covers an area 3 km (1.9 mi) wide.