A 'city-killer' asteroid got scarily close to Earth yesterday, and astronomers didn't know about it until it was just days away

Yesterday, a 427-foot-wide asteroid passed within 45,000 miles of Earth. Small asteroids canstrike Earth with the force of many nuclear weapons anddestroy entire cities. NASA…

Read More A 'city-killer' asteroid got scarily close to Earth yesterday, and astronomers didn't know about it until it was just days away