Now here’s an interesting question. What would happen if a small asteroid like 2008 TC3, the three-meter object that exploded in the atmosphere late Monday, were headed for a large city? We were able to judge with a high degree of confidence that 2008 TC3 would pose no threat to the surface, and indeed, early reports suggest that its energies — 1.1 to 2.1 kilotons of TNT — were expended in the atmosphere. But even the most confident scientists might be hard put to sell the case for calm if the public started imagining worse case outcomes.

David Morrison (NASA Ames) has written about the public response to a small impact scenario, a fact I’m drawing from the recent update of NEO News sent to me by Larry Klaes. Also available is a report from spaceweather.com of a visual sighting of the event, sent along by Jacob Kuiper, general aviation meteorologist at the National Weather Service in the Netherlands::

“Half an hour before the predicted impact of asteroid 2008 TC3, I informed an official of Air-France-KLM at Amsterdam airport about the possibility that crews of their airliners in the vicinity of impact would have a chance to see a fireball. And it was a success! I have received confirmation that a KLM airliner, roughly 750 nautical miles southwest of the predicted atmospheric impact position, has observed a short flash just before the expected impact time 0246 UTC. Because of the distance it was not a very large phenomenon, but still a confirmation that some bright meteor has been seen in the predicted direction.”

The best case scenario I can imagine for getting us to develop the tools needed for asteroid deflection is having the occasional small event like this making news around the globe. And indeed, we should have no shortage of events to point to, according to Don Yeomans, who toils at the Near-Earth Object Office at the Jet Propulsion Laboratory:

“We estimate objects this size enter Earth’s atmosphere once every few months. The unique aspect of this event is that it is the first time we have observed an impacting object during its final approach.”

Even so, we had little lead time, with the object being discovered only a day before its encounter with Earth. And if we found a much larger object on an equivalent course? We know that Tunguska-class events may occur as frequently as every 100 years, a grim reminder that space debris is wildly variable in size and can create catastrophe where it falls. Let’s hope it doesn’t take another Tunguska to awaken the public to the need for robust space-faring technologies that can nudge incoming asteroids into safer trajectories.

Emily Lakdawalla did an outstanding job on this story for the Planetary Society weblog. Let me quote from her thoughts on public reaction to a larger object:

But of course we now have to ask ourselves: what would have happened if the object was much bigger than 2 meters in diameter? Reassuringly, the first thing that would have happened is that the detection most likely would have happened much earlier. The bigger and more hazardous an object is, the brighter it is, and the sooner we will detect it. We will likely have way more than 20 hours’ warning of an incoming dangerous object. Still, though, the warning time for a tens-of-meter-diameter object could only be measured in days. If we’d had three days’ warning of a dangerous impactor heading for Sudan, what could the world have done? The remote location of the impact would have been fortunate for humanity in general, but disastrous for the few people who lived out in that remoteness. Could the developed world have done anything to prevent yet another humanitarian disaster from befalling the Sudanese?

These are highly theoretical questions at the moment, but they could become far more pointed at any time. All the more reason to be thinking, as the Association of Space Explorers continues to do, about the possibilities of crafting an international response. That one is dependent upon politics more than technology, and an equally tough challenge. For more on the public response to small impacts, see Morrison, D. “The Impact Hazard: Advanced NEO Surveys and Societal responses,” In Comet/Asteroid Impacts and Human Society (P. Bobrowsky & H. Rickman, eds.) Springer, New York (2007).