Isn't the latest Tunguska theory that a comet exploded in the atmosphere, not an asteroid hitting the ground?
http://www.space.com/scienceastronom...ry_011031.html
The researchers say the event was likely caused by a low-density asteroid that exploded in the atmosphere, sending out a firestorm that burned trees and a shock wave that did more damage, according to a story on the BBC's web site. The explosion was equal to more than 10 million tons of TNT, the researchers say.
http://www.planetary.org/programs/pr...steroid_alert/
The Planetary Society is helping plan an effective response to asteroid threats via our support of the B612 Foundation -- a recently created organization exclusively dedicated to this important work.
The Asteroid Impact Mapping System is a way of making the threats "real". Since, the corridors typically cross national boundaries, this system will also vividly show how this is a truly global danger requiring international coordination.