Sand Dunes and Ripples in Proctor Crater
The larger, darker bedforms are dunes composed of sand, most likely of fine size. Ripples tend to move slower than dunes. Because of this, over time, ripples get covered with dust, possibly explaining the bright tone visible here. The dunes are dark probably because they are composed of basaltic sand (derived from dark, volcanic rock) that is blown by the wind enough that dust does not sufficiently accumulate to change their color.
Image cutout is less than 5 km (3 mi) across and the spacecraft altitude was 253 km (157 mi). For full observation details including images with scale bars, visit the source link.
www.uahirise.org/ESP_011909_1320
NASA/JPL-Caltech/Arizona
Sand Dunes and Ripples in Proctor Crater
The larger, darker bedforms are dunes composed of sand, most likely of fine size. Ripples tend to move slower than dunes. Because of this, over time, ripples get covered with dust, possibly explaining the bright tone visible here. The dunes are dark probably because they are composed of basaltic sand (derived from dark, volcanic rock) that is blown by the wind enough that dust does not sufficiently accumulate to change their color.
Image cutout is less than 5 km (3 mi) across and the spacecraft altitude was 253 km (157 mi). For full observation details including images with scale bars, visit the source link.
www.uahirise.org/ESP_011909_1320
NASA/JPL-Caltech/Arizona