Tunguska Rethought

In 1906, something exploded in or above Siberia, leveling forest over a huge area. Many explanations-- some bizarre-- have tried to define exactly what exploded, but science has settled on a small asteroid as the likely culprit.

Now, running simulations on the supercomputer at Sandia National Labs, scientists suggest the asteroid responsible may have been even smaller than thought-- perhaps only 65 feet across.

If correct, that would make such disasters extremely difficult to defend against. The key to asteroid defense is detecting dangerous bodies well before they're on final approach to Earth. Finding and tracking such a body only feet wide may be beyond our capability for some time.

On the other hand, Tunguska-type events are rare, at least in human terms. They obviously are not wotld-enders. A Tunguska event could obliterate a major city, but by themselves they threaten neither the biosphere nor civilization. Finally, a robust, spacefaring civilization could almost certainly deal with such a small body even if it were zeroed in on its target.

If things fall right, humans might be only a century or so away from having built such a civilization.