One year ago this February, a 20-metre chunk of space rock hit the Earth over Chelyabinsk, Siberia. Shining brighter than the Sun, its fall was recorded by video ­cameras more than 400 miles away. Thousands of people in Chelyabinsk ran to their windows to see what that bright light was; a few moments later, the impact’s sonic boom arrived and shattered those windows. More than 1,500 people were hurt by flying debris. Forty-five miles west of Chelyabinsk, an eight-metre-wide hole was found in the ice of Lake Chebarkul; last summer, a half-ton meteorite was recovered from the lake bottom. It is not every day that a rock with half a megaton of energy hits the Earth above a major city (a million people live in Chelyabinsk). But near-Earth asteroids are hardly rare. The Minor Planet