How would we save the planet from a killer asteroid?

Gravitational Tugboat

The wonderful thing about space is that physics becomes a strange and idealized thing. If you imagine trying to tug a multi-million-ton rock out of the way on Earth, it seems nearly impossible. But in space, friction ceases to exist. Bodies move about as dictated by gravity. So, if you put something heavy near an asteroid, you can pull it off track.

This method happens slowly. It would only change the asteroid’s course at a rate of millimeters or centimeters per second per year. So you need a lot of lead time. But should we happen to find a monster asteroid out there heading toward us with a hundred years of lead time, this method is the safest and easiest way to deflect it.

As a reverse tugboat, scientists have also considered ion beam shepherding. This basically means having a spacecraft fly alongside the asteroid and pelt it with plasma, thereby shoving it aside. Of course, the spacecraft needs to be constantly pushing itself closer at the same time, or the “equal and opposite reaction” effect in physics would simply have the spacecraft pushing itself away in equal measure. Much like the gravity tractor method, this is slow but predictable and possible using technology that already exists.

Or, as a simpler version of that idea, other scientists have suggested simply painting an asteroid white to increase its reflectivity. This equates to more photons from the sun bouncing off its surface, and the extra pressure would serve to gradually move it off course.

Dismantling an Asteroid

There are other, more outré methods, as well.

We could blast it with a laser, for example. The goal here isn’t really to destroy the rock (though that would be part of it) but more to shove it with the laser and use the bits that flake off to help further propel the asteroid away from the laser. But since we don’t currently have a giant space laser, this method requires a bit more planning.

Another option is commonly called a mass driver. This takes the “equal and opposite reaction” to its logical conclusion. In its most basic form, imagine a catapult hurling rocks off of an asteroid. Physics dictates that as you hurl small boulders toward the Earth, the asteroid itself will slide away from us.

All of these methods require some advance warning. The good news is that asteroids large enough to end life on Earth are big enough to spot, so we’ll have plenty of time both to panic and to plan.

Korey Haynes is an Astronomy contributing author.

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