A BIG ASTEROID NEARLY HIT THE EARTH the other day, and nobody but Ken Layne noticed. Well, him and some astronomers.

Just a little over a week ago I noted that an unexpected asteroid strike might set off an accidental nuclear exchange. Little did I know that this thing was bearing down on us as I wrote. And it came close:

What is most shocking is just how close it came to Earth. This is only the sixth known asteroid to penetrate the Moon’s orbit, and by far the biggest. According to Brian G. Marsden (Harvard-Smithsonian Center for Astrophysics), the object came within 120,000 kilometers (0.0008 astronomical unit) of impacting Earth.

Though the exact details of an impact scenario depend on the rock’s composition, had it hit Earth the event would have been been “Tunguska-like,” with a force rivaling the largest H-bombs.

Yeah, if it’s Tunguska-like it would be bigger than any H-bomb ever exploded. Not a civilization-ender, but bad, bad, bad. (And it was close — follow the first link on this post and look at the to-scale diagram of just how close.) Upshot:

A disturbing detail is that 2002 MN was discovered three days after its closest approach. Though we are almost certainly out of harm’s way from this near Earth object (no potential impacts are forecast until at least 2050), its late detection may be telling. Currently there is no dedicated Southern Hemisphere NEO search program, and NASA is currently focused on finding bodies greater than 1 kilometer across.

We need to extend our “preemption” strategy to these threats.

UPDATE: Just noticed this thread about the subject on Slashdot.

BTW, why can’t we have a nice fat comet hit Mars and leave behind a lot of convenient water and organics. I think a comet around 100km in diameter (okay, that’s a really, really big comet) would be enough to halfway terraform Mars all by itself.