Astronomers have identified numerous asteroids big enough to cause a catastrophe for the entire plane None is on course to do so in our lifetimes, but there are many smaller asteroids that could strike in the near future, with devastating effects. On June 30, 1908, an object the size of a 15-story building fell in Tunguska, a remote part of Siberia The object an asteroid or a small comet exploded several kilometers before impact, burning and blowing down trees across 2,000 square kilometers(800 square miles) Clouds of tiny particles of dust and ice filled the sky. The particles reflected the sun's light onto the Earth, and for days people in Europe could read newspapers outdoors at night.