A “city killer” asteroid isn’t science fiction, it’s a real risk. Project Leader at The Aerospace Corporation Nahum Melamed explains that though these events are statistically rare, history shows they can happen. In 1908, a roughly 50-meter asteroid exploded over Siberia in what’s known as the Tunguska event, flattening more than 800 square miles of forest. Had that airburst occurred over a major metropolitan area, the destruction would have been instantaneous. Preventing that kind of devastatio