The Richat structure stretches almost 30 miles across the Sahara Desert in Mauritania. The image was captured with instruments aboard the Terra satellite.
Image Credit: NASA/GSFC/METI/Japan Space Systems/ASTER
The looming bull's eye above can be easily seen from orbiting satellites including the International Space Station. Known as the Richat Structure — or the Eye of the Sahara — this geologic formation has a diameter nearing 50 kilometers.
Partly due to its circular shape, scientists originally suspected that the formation was the site of an impact crater resulting from a high-speed asteroid. After studying the formation, however, scientists found little evidence suggesting such an impact. Instead, researchers now believe that erosion gave rise to the formation, but there's still no full explanation for its spherical symmetry.