I don’t know the statistics for events like this, but I’d like to. In any case, two Tunguska-sized objects zipping by at less than one-fourth the distance to the Moon only 16 days apart has got to be uncommon.
Events like this probably happen every couple of years on the average, but March 2009 has been marked by the very close approach of two potentially hazardous objects that were only discovered when it was too late to avoid their impacts. Imagine the Tunguska event of 1908 repeated in a populated area or in an ocean region where it could cause a tsunami.
Tonight, the object known as 2009 FH will come within 85,000 km of Earth. Details at SpaceWeather.com.
Fred Bortz, author of Collision Course! Cosmic Impacts and Life on Earth and other books for young readers