Apr 17 2009

Saving the Earth from an Asteroid

In Death From The Skies, Phil Plait discusses all the ways in which the universe might wipe out life on Earth. Perhaps the most obvious is by asteroid or comet impact. This one comes readily to mind probably because the current majority opinion is that the dinosaurs met their end at the hands of a large asteroid striking the earth near modern-day Mexico. This has also been the plot of two recent movies – Deep Impact and Armageddon, with nice visual effects of the impact.

Most readers are probably aware of the fact that the Earth is threatened by asteroids which cross our orbit. There are none right now on a known collision course with the Earth, but the threat remains. Apophis will come close in 2029 and 2036, but probably won’t hit. But eventually a large¬† asteroid’s path will intersect the Earth again – it’s just a matter of time.

Therefore astronomers have been thinking about ways to protect the earth from such an inevitability. One feature of any scheme to protect the Earth is the tracking of all near-earth objects. We cannot protect ourselves from a threat if we don’t know it exists. Also, the more lead time we have, the easier it will be to deflect an incoming rock.

But what do we do if we detect an impending impact? There are numerous suggestions, and recently aerospace engineer, David French, has suggested a new one.  He proposes attaching a heavy object by a long tether to the asteroid. This, he argues, will shift its center of gravity and thereby alter its trajectory. Given enough time, and a long enough tether (from 1,000 to 100,000 kilometers) even a large asteroid could be made to miss the Earth.

This sounds like a plausible method. I leave it to the astronomers to do all the tricky calculations, but I don’t see anything wrong with the basic concept. The engineering, however, seems non-trivial. It would be difficult to manufacture such a long tether (probably only doable with carbon nanotubes, which we cannot yet make indefinitely long). Also, many asteroids are tumbling and it seems to me this would make it difficult to attach the tether and keep it extended, rather than just wrapping around the asteroid as it spins. Tricky – but not impossible.

What other methods have been proposed? Probably the first one people think of, and the one used in the movies, is to just blow up the asteroid with nukes. This makes for good cinema, but is not very practical. It would take quit a bit of power to blow up a solid rock or hunk of metal. Further, the explosion is unlikely to pulverize the asteroid. Rather, it would more likely just break it up into many pieces, most of which would still hit the Earth, perhaps doing more total damage than the single impact.

Attaching a rocket to the asteroid and blasting it to a different trajectory makes sense, but would be technically difficult to impossible for most asteroids. As I said, asteroids tend to tumble, which would make the timeing of firing the rockets tricky and limit their total time for firing.

Perhaps the most intersting suggestion I have read is to use a gravitational tug – to have a rocket not attached to the asteroid, but next to it. The rocket would fire with just enough power to suspend it above the asteroid, counteracting its gravitational attraction. The rocket’s gravity would then provide a slow steady tug on the asteroid. If we have a few years warning, this technique could work even for large asteroids.

Yet another method is to paint the asteroid so that it reflect more sunlight, and therefore gets a little push from the sun which might nudge it far enough to miss the Earth.

Perhaps my favorite suggestion is to just mine the asteroid. Land one or more mining ships on the asteroid, break it up into ore, and cart it away to the Moon or somewhere else where the metals can be used to construct a station or something else. The asteroid will then just cease to exist, and we get the minerals to boot.

These are all technically challenging methods, and it may be years before we could pull any of them off. Efforts are already underway to track all near Earth objects, and this is good, because lead time will be critical no matter what method we use. If we had enough advance warning, I am confident that we have the technology currently to develop one of these methods to thwart the incoming asteroid.

One thing is for sure – any of these methods, based in science and technology, are more likely to work than having the world’s “psychics” use their telekinetic powers to push the asteroid away, or by having practitioners of “The Secret” wish it away.

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