The impact of an asteroid or comet in the Sahara Desert of northern Chad.

The impact of an asteroid or comet several hundred million years ago, according to scientists, left scars in the landscape that are still visible in this International Space Station/Expedition 12 picture of an area in the Sahara Desert of northern Chad. The concentric ring structure is the Aorounga impact crater, with a diameter of about 17 kilometers (10.5 miles). The original crater was buried by sediments, which were then partially eroded to reveal the current ring-like appearance. Scientists note a number of valleys cut by thousands of years of wind erosion. The area shown is centered at approximately 19.1 degrees north latitude and 19.3 degrees east longitude.