Atrueoriginall got it right in the second comment from the top. In June 2009, Cornell scientists confirmed the Tunguska event was caused by a comet. See http://thefutureofthings.com/pod/7494/tunguska-mystery-solved.html and Atrueoriginall's link at http://www.dailygalaxy.com/my_weblog/2009/06/nasa-space-shuttle-solves-mystery-of-earths-greatest-explosion-the-1908-tunguska-event-in-siberia.html