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Boston University researcher Farouk El-Baz spotted the crater whilst studying satellite images of the area with colleague Eman Ghoneim.
The crater has two rings, the outer of which is around 31 kilometres across. The previous largest-known Saharan crater was around twelve kilometres across. For comparison, the Meteor Crater in Arizona, USA, is just 1.2 kilometres wide and the Chicxulub crater in the Yucatan Penninsula (that may have been formed by a dinosaur-killing comet or asteroid) is around 160 to 240 kilometres wide.
El-Baz used to work on NASA�s Apollo missions, and recognised the crater as being reminiscent of the many double-ringed craters on the Moon. He believes that an asteroid that may have formed it could have been 1.2 kilometres wide (as large as Arizona�s Meteor Crater).
El-Baz has named the crater 'Kebira', which means 'large' or 'great' in Arabic. His team is speculating why the crater has not been spotted before.
"Kebira may have escaped recognition because it is so large � equivalent to the total expanse of the Cairo urban region from its airport in the northeast to the Pyramids of Giza in the southwest," said El-Baz. "Also, the search for craters typically concentrates on small features, especially those that can be identified on the ground. The advantage of a view from space is that it allows us to see regional patterns and the big picture."
Kebira lies in the southeast of Egypt, right on its border with Libya. The crater�s features have been altered by significant wind and water erosion. "The courses of two ancient rivers run through it from the east and west," said Ghoneim.
The crater may also explain the presence of tiny, yellow-green beads of glass in a 60-by-100 kilometre area in Egypt, also near its border with Libya. Studies on the beads suggested they were formed in an asteroid impact, but no corresponding crater was found. Such beads are thought to form when a massive asteroid crashes into the Earth and the high temperatures of impact vaporise the rock at the impact site. The rock then rains back to Earth as drops of glass.
The images were taken by NASA�s Landsat satellite.
More info: Boston University Center for Remote Sensing
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