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Richat Structure, Mauritania
The Richat Structure in Mauritania is a gigantic circular swirl, about 30 miles (50 kilometers) in diameter, that forms a bull’s-eye in an otherwise featureless expanse of west African desert. When astronauts first noticed the Richat Structure in the 1960s, it was believed to be a crater left behind by an immense meteor, because of the uniformity of its curves. But scientists now think that it’s a rock formation of Paleozoic quartzites, laid bare by erosion. Either way, though, it’s plenty strange looking.
