This image of the Richat structure in Mauritania was acquired on 21 June 2003 by Envisat's Medium Resolution Imaging Spectrometer (MERIS) in full resolution mode, meaning a spatial resolution of 300 metres.

The 50-km-diameter circular Richat structure is one of those geological features that are more clearly observed from space than from down on the ground, with this 'eye of Africa' a familiar landmark to astronauts since the earliest manned missions.

Once thought to be the result of a meteor impact, today researchers believe the Richat structure was caused by process of geological uplift followed by erosion from wind and water.