Image Credit: NASA/GSFC/METI/Japan Space Systems, and U.S./Japan ASTER Science TeamExplanation: What on Earth is that? The
Richat Structure in the
Sahara Desert of
Mauritania is easily visible from space because it is nearly 50 kilometers across. Once thought to be an
impact crater, the
Richat Structure‘s flat middle and lack of shock-altered rock indicates otherwise. The possibility that the
Richat Structure was formed by a
volcanic eruption also seems improbable because of the lack of a dome of
igneous or volcanic rock. Rather, the layered
sedimentary rock of the Richat structure is now thought by many to have been caused by uplifted rock sculpted by
erosion. The
above image was captured by the
ASTER instruments onboard the orbiting orbiting
Terra satellite. Why the
Richat Structure is nearly circular remains a mystery.