Tricky Craters

Countless numbers of space rocks have blasted Earth over its long history. These collisions gouge holes in the ground, known as impact craters. Wind and rain erase most of them, but a few survive. And scientists continue to search for more. One problem, though, is how to tell when a big, round hole in the ground is an impact crater and when it’s just a big, round hole in the ground.
In the last decade, for example, two possible impact craters were discovered in Egypt.
The first was discovered 10 years ago. Satellite photos revealed a round structure that’s almost 20 miles wide. Such a crater would have been formed by an asteroid almost a mile in diameter.
Because the crater is so remote, it took a while for scientists to get to it. When they did, they found no evidence of an impact. The rock hadn’t been subjected to a powerful shock, for example. So the feature’s origin remains unknown.
Another crater was spotted a couple of years later. It’s only about 150 feet across. But its ri