A half million years ago, Antarctica was hit by a blowtorch from space

Sometime a bit less than a half million years ago, a decent-sized asteroid impacted over Antarctica. But it didn't hit the ground. Instead, it vaporized high above Earth's surface and created a white-hot blowtorch of superheated gas that touched down on the ice and released energies similar to that of a nuclear bomb.

The evidence for such a big event is surprisingly subtle: Scientists have found tiny spheres of rock and iron on the top of a mountain in coastal Antarctica. They're small, not muc...