Eye of the Sahara

This is the Richat Structure, found in the Maur Adrar Desert of Mauritania in Africa. Also known as the Eye of the Sahara, it has a diameter of almost 50 km, and is one of Earth's only natural formations still visible from space. It was originally thought to be an impact crater, and then an eroded volcano, but current speculation suggests that it's a circular dome of layered sedimentary rocks laid bare by erosion. Exactly why it's such a perfect circle, however, remains a mystery.

False-color composite image by NASA/GSFC/USGS EROS Data Center

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