It is more than twice the size of the next largest Saharan impact depression and more than 25 times the size of Arizona's famous Meteor Crater.

The American team that found it says its sheer size may have helped it escape detection all these years.

The structure, which has an outer rim surrounding an inner ring, has been named "Kebira", which means "large" in Arabic and also relates to the crater's physical location on the northern tip of the Gilf Kebir region in southwest Egypt.

"Kebira may have escaped recognition because it is so large," said Dr. Farouk El-Baz, director of the Boston University Center for Remote Sensing, where the find was made.