Taking advantage of lengthening shadows during the onset of winter and at different times of day, NASA's Mars Exploration Rover Spirit acquired this series of images accentuating subtle features in the terrain. Images acquired at low sun angles allow scientists to better understand differences in surface roughness among soils and rocks. Variations in how brightly sunlight reflects off surfaces under different lighting conditions help scientists estimate the microscopic physical characteristics of the mineral grains in different rocks and soils.
Spirit acquired these sets of images at different local true solar times (LTST) on martian days, known as sols, 930 (Aug. 15, 2006), 931 (Aug. 16, 2006), and 935 (Aug. 20, 2006) using the 601-nanometer filter of the panoramic camera. Spirit acquired the single-frame images of sand ripples with the panoramic camera turned to an azimuth of 290 degrees (west-northwest).