Get ready for a near-miss experience, 24 years from now

We cannot destroy the Earth. Regrettably the reverse appears not to be true. A most amusing web site (ned.ucam.org/~sdh31/misc/destroy.html) says, "The Earth was built to last. It is a 4,550,000,000-year-old, 5,973,600,000,000,000,000,000-tonne ball of iron. It has taken more devastating asteroid hits in its lifetime than you've had hot dinners..." But speaking of asteroid hits, Monday's Citizen says 300-metre-wide "2004 MN4" will whoosh past in 2029 just 24,000 to 40,000 kilometres away, "close enough to be seen by the naked eye."

I don't mean to cause panic here, so please walk slowly to the cemetery. But the moon is 400,000 kilometres away and some scientists worry whenever anything lethally huge passes within twice that distance. Which is surprisingly often. Bill Bryson's excellent A Short History of Nearly Everything calls an asteroid missing by 106,000 miles "the equivalent of a bullet passing through one's sleeve without touching the arm." So 24,000 kilometres is like having it go between your hat and your head.

The Citizen says astronomers "are sure it will miss," but Earth's gravity "might put 2004 MN4 on course for a collision in 2034 or a year or two later." Whaddaya mean, "might"? I thought scientists had a pretty good handle on stuff like orbits.

Superstring theory may be a jury-rigged, 26-dimensional mess, but the lab coats know exactly when, where and why Jupiter will next align with Mars. However, there's a surprising amount of "uncertainty" about asteroids, though NASA (neo.jpl.nasa.gov) gives the exact day (April 13, 2029) they're totally convinced 2004 MN4 will miss us and then do who knows what. Which is one reason, Mr. Bryson says, that those films where they spot a killer asteroid heading for the Earth and blast it apart in an inspiring international effort that ushers in an era of global peace and co-operation are a tad unrealistic.

No, not the Age of Aquarius bit. The science. We don't have rockets to carry nuclear warheads into space, an asteroid arriving in chunks isn't that much better, and we can't predict orbits well enough to know which way to deflect it if at all even if we see it in time.

Hold on, I hear you cry. What's this last "if"? Surely we're looking out for giant space rocks of death? No. Not really.

A few years back, I noticed scientists' habit of looking up from their telescopes and saying: What do you know, this incredibly huge rock just went by, sorry we didn't mention it sooner. As a June 21, 2002 Citizen story explained, "There is no program searching for NEOs (Near-Earth Objects) approaching the southern hemisphere and NASA ... only looks for bodies bigger than a kilometre."

Mr. Bryson adds those objects would be hard to see even if more people were looking. So from a clear blue sky, in one second, we're vapourised and a giant wall of flaming debris is roaring toward Nebraska.

You may object that it wouldn't, technically, amount to the Earth destroying us. But with us orbiting the Sun at 105,000 km/h, it's a bit like hitting a moose with your car: The moose gets some credit, but you do most of the actual work.

Still, don't panic about the sky. For one thing, Scientific American says the chance of Earth copping a civilization-ending asteroid in any given human lifetime is just one in 5,000, though a city-masher, well, who knows? For another, Mr. Bryson says from what little we know it's even worse under our feet. For instance, those kimberlite pipes they find diamonds in: Are they next to the kimberlite cigars, or like kimberheavy pipes but less dense? No. "(D)eep in the Earth there is an explosion that fires, in effect, a cannonball of magma to the surface at supersonic speeds. It is a totally random event. A kimberlite pipe could explode in your backyard as you read this."

One didn't in my case, but you never know. Also, he says, Yellowstone Park is one gigantic volcano prone to sporadic vast eruptions, possibly including one of those six-years-of-darkness-everyone's-dead-Dave kind of events. Recently, a lake in Yellowstone tipped. Weird, huh? Plus there's earthquakes, tsunamis, landslides ...

In short, the killer asteroid will probably arrive too late, especially if you eat lots of fatty foods. And space also stocks gamma-ray bursts, sinister clouds of dust and many other ha-ha-remember-life-on-your-planet novelty items.

So if you can do a good deed, do it now before Earth's magnetic field weakens and the cosmic rays come to lunch. And forget riding it out in a backyard bunker. Remember: kimberlite.

[First published in the Ottawa Citizen]