11 June 2004
These four Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images show north polar sand dunes as they appeared on four different days over the past ten weeks. In summer, the dunes would be darker than the substrate on which they occur. However, it is currently spring in the northern hemisphere, and the dunes are still covered with frost from the previous winter. The MGS MOC has been busy over the past several months, documenting the changes in frost patterns that occur on dunes and interdune substrates all over the north polar region. The site shown here was imaged on 30 March, 23 April, 16 May, and 9 June 2004. The bright frost that covers the dunes progressively changes from one image to the next, as dark spots develop and frost sublimes away. This defrosting dune monitor site is located near 80.0°N, 237.5°W. Each strip is about 1.1 km (0.7 mi) wide and illuminated by sunlight from the lower left.