The wonderful thing about space is that physics becomes strange and idealized. If you imagine trying to pull a multi-million dollar rock out of the way on Earth, it seems almost impossible. But in space, friction ceases to exist. The bodies move as dictated by gravity. So, if you put something heavy near the asteroid, you can pull it out of the track.
This method is slow. This will only change the course of the asteroid at the speed of millimeters or centimeters per second per year. So you need a lot of time. But if we manage to find an asteroid monster there, heading towards us for a hundred years, this method is the safest and easiest way to reject it.
Scientists also considered an ion beam cartridge as a reverse tug. This basically means that the spacecraft flies near the asteroid and melts it with plasma, thereby repelling it. Of course, a spacecraft must constantly approach it at the same time, or the effect of an “equal and opposite reaction” in physics would simply drag the spacecraft equally. Like the gravity tractor method, this is a slow but predictable and possible use of technology that already exists.
Or, as a simpler version of this idea, other scientists suggested simply painting a white asteroid to increase its reflectivity. This equates to more photons from the sun bouncing off its surface, and the additional pressure will gradually move it off course.
There are other, more advanced methods.
For example, we could run it with a laser. The goal here is not to destroy the rock (although it would be part of it), but more to shove it with a laser and use bits that exfoliate to help move the asteroid from the laser. But since we currently do not have a giant space laser, this method requires a bit more planning.
Another option is usually called a mass driver. This leads to an “equal and opposite reaction” to its logical conclusion. In its most basic form, imagine a catapult throwing stones from an asteroid. Physics dictates that when you throw small boulders to Earth, the asteroid itself will move 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 large enough to make out, so we will have enough time to panic and plan.
Kore Haynes – astronomy the author.