The Daily Galaxy
Thu, 15 Dec 2011 13:13 CST
Boston University scientists sifting through satellite photos found the largest crater seen to date in the Great Sahara Desert of North Africa. The 100-million-year old crater, known as Kebira, which means "large" in Arabic, is 19 miles wide.
The crater is on the northern tip of the Gilf Kebir region of southwestern Egypt near Libya. The meteorite that gouged out Kebira probably was three-quarters of a mile wide. The terrain around the crater is 100 million year-old sandstone. Two ancient rivers run through the crater site from the east and west.
The shock of such a large object crashing into Earth tens of millions of years ago may have left behind the field of yellow-green silica chips - the mysterious desert glass - seen today on the surface among the giant dunes of the Great Sand Sea in southwestern Egypt.
As a geologist who had spent most of his career studying the Earth's major deserts, Dr. Farouk El-Baz, now the director of the Center for Remote Sensing at Boston University, knew that the glass formed after a massive meteorite hit the desert with enough energy to splatter chunks of melted sand across the extensive fields where fragments are common today. But beyond the glass, no evidence of such an impact had ever been found. El-Baz decided to take another look at satellite data of the Western Desert to see if he could find the elusive crater.
El-Baz sorted through image after image of the Western Desert when he came across a ring of rocks surrounded by traces of an outer ring: the telltale markings of an impact crater. He called Boston University research associate Eman Ghoneim, and she agreed that the image revealed a crater. The massive crater measured 31 kilometers across and was large enough to contain 70,000 football fields.
By contrast, the Chicxulub Crater left on the Yucatan Peninsula by the meteorite believed to have caused the extinction of the dinosaurs is ten times larger than Kebira, measuring 150 to 300 kilometers wide.
But why had no one noticed the giant Kebira crater before? El-Baz speculates that the crater's massive size hid it in plain view. "The search for craters typically concentrates on small features, especially those that can be identified on the ground," he said."The advantage of a view from space is that it allows us to see regional patterns and the big picture."
Earth Observatory, NASA