Tunguska revisited

Uh-oh. A new study suggests that the asteroid/comet that caused the infamous devastation at Tunguska in Siberia a century ago may not have been as large as previously thought. There are a lot more small rocks floating around out there than there are big ones...

ALBUQUERQUE, N.M. - The stunning amount of forest devastation at Tunguska a century ago in Siberia may have been caused by an asteroid only a fraction as large as previously published estimates, Sandia National Laboratories supercomputer simulations suggest.

"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. "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."

Because smaller asteroids approach Earth statistically more frequently than larger ones, he says, "We should be making more efforts at detecting the smaller ones than we have till now."

The new simulation - which more closely matches the widely known facts of destruction than earlier models - shows that the center of mass of an asteroid exploding above the ground is transported downward at speeds faster than sound. It takes the form of a high-temperature jet of expanding gas called a fireball.

This causes stronger blast waves and thermal radiation pulses at the surface than would be predicted by an explosion limited to the height at which the blast was initiated.

"Our understanding was oversimplified,' says Boslough, "We no longer have to make the same simplifying assumptions, because present-day supercomputers allow us to do things with high resolution in 3-D. Everything gets clearer as you look at things with more refined tools."

There's a good bit more at the other end of the link. As if global warming wasn't enough to worry about.