Outdoing the dinosaurs: What we can do if we spot a threatening asteroid

That’s a lot of ifs. Compounding these issues is that predicting future orbits for such tiny objects is notoriously complicated. Yes, we may successfully throw a potentially Earth-crossing asteroid off course… into a new orbit that is all but guaranteed to strike our planet at some later date.

One of the ways this nonintuitive behavior is possible is through what are called keyholes. The gravitational environment of the solar system is complicated and ever-shifting, with every point in space influenced in some way by the arrangements of the massive planets. Most orbits within the Solar System are stable and predictable. But there are certain regions—the keyholes—where predicting future trajectories are almost impossible. The gravity is so complex in the keyholes that orbits become chaotic. An asteroid can enter a keyhole in one direction and come out in almost any other. The tiniest of changes to an asteroid’s orbit, say, from uneven surface heating due to slight color changes across the face of the asteroid, can lead to wildly different orbits if they take it through a keyhole.

So if we go about the game of deflecting asteroids, we have to ensure that their new trajectories don’t take them near any keyholes. If they do, we may just be jumping from one disaster to another—possibly one that allows way less time to react and prepare.

I don’t want to miss a thing

But maybe we could take dangerous asteroids and…blow them up. Yes, that is the plot of Armageddon. No, there will likely not be a rocking soundtrack to accompany the mission.

Altering trajectories of fast-moving, massive asteroids is hard. We need a lot of warning, and we have to make sure our calculations are on point.

The danger of a giant asteroid comes directly from its size, as it has more kinetic energy to deliver to our planet. A smaller rock traveling at the same speed would simply burn up in our atmosphere. That’s the driving logic behind PI, a new planetary defense initiative funded by NASA’s Innovative Advanced Concepts Program (disclosure notice: I serve on the advisory council for this program, so of course I think it’s cool).

The idea behind PI is simple. We find a large asteroid on a dangerous trajectory. We load a big bomb (preferably nuclear) on a rocket. We shoot it at the asteroid. The rocket buries itself as deeply as possible into the asteroid and blows up, fragmenting the large asteroid into many smaller ones.

Multiple studies have shown that most asteroids are “rubble piles”—just loose collections of boulders barely clinging together through their mutual gravitational attraction. If we were to try to blow up an asteroid, a few of those boulders would be flung away. Most of the asteroid would likely expand into fragments traveling on the same trajectory—a cosmic grapeshot.

But if we did it right, those smaller fragments would just burn up in our atmosphere, transforming an end-of-days killer asteroid into the most magnificent meteor shower the world has ever seen. Of course, this is just an interesting idea right now, still in the simulation phase.

We have our work cut out for us if we’re going to find a way to defend ourselves when our cosmic time is up.