A team at Sandia National Laboratory in Albuquerque, N.M., has found that the Tunguska explosion in 1908 was caused by a much smaller asteroid than previously calculated. The new assessment has used powerful supercomputers to grind out high-resolution 3D simulations that more realistically model the blast's effects. Sandia is a National Nuclear Security Administration laboratory.

“The asteroid that caused the extensive damage was much smaller than we had thought,” says Sandia principal investigator Mark Boslough of the impact that occurred June 30, 1908. The event occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai of Russia, at 7:40 a.m.

“That such a small object can do this kind of destruction suggests that smaller asteroids are something to consider. Their smaller size indicates such collisions are not as improbable as we had believed.”

The 1908 explosion leveled an estimated 80 million trees over some 830 square miles, and it is estimated to have measured 5.0 on the later-designed Richter scale. The Tunguska hit is the largest impact event in recent history. It was calculated that if the collision had occurred 4 hours 47 minutes later, it would have completely destroyed the Imperial Russian Capital City of Saint Petersburg (Leningrad).

What scientists had previously thought to be an explosion between 10 and 20 megatons is now more likely to have been only three to five megatons. This means that it may become necessary to track smaller asteroids for defensive purposes.

“Any strategy for defense or deflection should take into consideration this revised understanding of the mechanism of explosion,” says Boslough.

Tunguska-scale events are estimated to occur only once every several centuries. Most of them likely take place over oceans or unpopulated areas, but as Earth's population gets denser the risk of massive human losses will be significantly higher.