Aorounga Impact Crater
February 11, 2002
The impact of a piece of an asteroid or a comet, several hundred million years ago, left scars in the landscape that are still visible on this space-borne radar image of an area in the Sahara Desert of northern Chad (centered at 19.1 degrees north latitude, 19.3 degrees east longitude). The concentric ring structure is the Aorounga impact crater, with a diameter of about 17 kilometers (10.5 miles). North is toward the upper right. It's possible that Aorounga is one of a string of impact craters formed by multiple impacts.The above image was acquired by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) on April 18, 1994, on-board the space shuttle Endeavour. Radar imaging is a valuable tool for the study of desert regions because the radar waves can penetrate thin layers of dry sand to reveal details of geologic structures that are invisible to other sensors operating in different wavelengths. The original crater was buried by sediments, which were then partially eroded to reveal the current ring-like appearance. Dark streaks on the image are deposits of windblown sand that are migrating along valleys cut by thousands of years of wind erosion. On this image, different radar frequencies are assigned different colors; L-band (1.25 GHz) is red, C-band 5.3 GHz) is green.