What would happen if asteroid 99942 Apophis ever hit the Earth? It’s about 1200 feet in diameter, and according to David Morrison (NASA Ames), that’s large enough to obliterate an area the size of England. The subject was under discussion at the recent American Association for the Advancement of Science meeting, and is reported capably in this Columbus Dispatch story, which quotes others on their own conclusions.

Jay Melosh, a geophysicist at the University of Arizona’s Lunar and Planetary Laboratory, said that if Apophis struck Earth, it would produce a 40-megaton blast, almost eight times larger than the most powerful nuclear bomb ever detonated. The explosion would create a crater more than 2 miles wide and obliterate buildings and bridges in a 4-mile radius. Melosh said everything around it would be buried beneath 20 inches of debris.

Nice to see a sober article discussing asteroid deflection in the popular press. Apophis probably isn’t going to make this kind of history, but the potential for getting blind-sided by an uncatalogued object is always there. Long-term thinking inevitably includes the premise of species survival, which is why a space-based infrastructure will eventually be forced upon us whether we want it in the short-term or not. Let’s hope it doesn’t take a Rendezvous with Rama-type survivable hit to make the case more emphatically.

Addendum: New Scientist covers Apophis scenarios and asteroid deflection in this recent article. Also see this post by Brian Wang on the Lifeboat Foundation weblog.