In eastern Arabia lies an anonymous crater, 120 kilometers (75 miles) across. The floor of this crater contains a large exposure of rocky material, a field of dark sand dunes, and numerous patches of finer-grain material, probably dust. The shape of the dunes hints that prevailing winds have come from different directions over the years.
This false-color image, made from frames taken by the Thermal Emission Imaging System (THEMIS) aboard NASA's Mars Odyssey orbiter, shows the center of the crater's floor. The image combines a daytime view at visible wavelengths with a nighttime view at infrared (heat-sensing) wavelengths, thus giving scientists clues to the physical nature of the surface.
Fine-grain materials, such as dust and the smallest sand particles, heat up quickly by day and cool off equally quickly at night. However, coarser materials - bigger sand particles, gravel, and rocks - respond more slowly to the same daily cycle.
This means that when THEMIS views these late in the martian night, they appear warmer than the pools and patches of dust. In the image here, areas that are cold at night appear in blue tints, while the warmer areas show in yellows, oranges, and reds.
Location: 26.7N, 63.0E Released: 2006/02/07 Instrument: VIS Image Size: 37.7x34.2 km, 23.4x21.3mi, 2092x1907 pixels Resolution: 18m (59ft.)
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