7 June 2004
Presently, it is autumn in the southern hemisphere of Mars. Sand dunes at high and middle latitudes are becoming cold and frosted. This frost, probably water ice, is persistent enough that it is still present around 2 p.m. in the afternoon, when Mars Global Surveyor (MGS) flies over these dune fields. This MGS Mars Orbiter Camera (MOC) image shows an intracrater dune field at 59.4°S, 158.9°W, as it appeared last week on 3 June 2004. In summer, these dunes would be very dark relative to the substrate on which they occur. In autumn, as shown here, they begin to accumulate frost that will last through the coming winter. Southern hemisphere winter will arrive around 20 September 2004. The image covers an area about 3 km (1.9 mi) across and is illuminated by sunlight from the upper left.