Our First Line Of Asteroid Defense? Paintballs!


Imagine: An asteroid has been discovered. Scarily, it’s a big ol’ hairy extinction-level asteroid. You know, the kind of asteroid that gave the dinosaurs a really bad day 65 million years ago. Astronomers think there’s a high probability that it will hit us in 20 years time. What do we do?

(Cue screaming people running through the streets, riots, looting, orgies, awesome doomsday parties…)

Once the inevitable panic has died down, no doubt the world’s population will start asking their governments what they intend to do about it. At that moment, as the horrid sinking sensation sets in, politicians will wish they’d invested more money into their space programs. “Whaddaya know. We needed that space infrastructure after all! What were we thinking all these years building bombs and war machines? It’s the UNIVERSE that’s going to kill us! What fools we’ve been…”


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Fortunately, despite the lack of political will to spend more on space technology over the years, space experts do have some clue as to how to deal with an incoming asteroid threat. And if that threat is 20 years out, we may actually have a stab at preventing the space rock from hitting us.

So what should we do?

For one thing, you can put your Armageddon-style nuclear warhead away — although I can think of no better use for the world’s aging nuclear deterrent — we need a far more subtle, long term solution.

Cue Sung Wook Paek, an MIT graduate student who won the 2012 Move an Asteroid Technical Paper Competition, sponsored by the United Nations’ Space Generation Advisory Council. In Paek’s answer to the asteroid threat, he proposes firing two volleys of paintballs at the space rock. And for his test scenario, he focused on asteroid Apophis.

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99942 Apophis is a 270 meter (885 ft) near-Earth asteroid that, for a brief time, became the biggest extraterrestrial threat to Earth. In 2004, initial observations suggested an uncomfortably high statistical probability that it may hit Earth in 2029. Fortunately for us, by 2006 further observations refined the asteroid’s orbit and a 2029 impact could be ruled out. But there’s another impact possibility in 2036, albeit a very, very small one.

By Paek’s reckoning, around five tons of white paint powder could be encased in pellets and, through two separate volleys, the majority of Apophis’ surface can be covered.

Of course, launching that much paint from the Earth’s surface would be expensive, so he suggests manufacturing it in space. A fully-loaded spaceship — the cosmic equivalent of a paintball gun or spray paint can — would then approach the asteroid, take station a certain distance from it, and release the first volley of paintballs. It would then wait for the asteroid to spin on its axis 180 degrees and release a second volley. The entire surface would then be covered by a thin layer of paint approximately five-micrometers thick. A short video showing the process can be seen below.

What’s the point of giving Apophis a paint job? That’s the clever bit.

As light from the sun hits an object, a minuscule amount of pressure is applied — each individual photon exerts a small amount of momentum to the object’s surface. If the object is dark (i.e. if the object’s albedo is low), more photons are absorbed; if it’s light (i.e. the albedo is high), more photons are reflected. By changing the albedo of an asteroid like Apophis, it’s theoretically possible to change how sunlight interacts with it. The greater the brightness, the greater the reflected light, the greater number of photons reflected, the greater the solar radiation pressure.

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This radiation pressure may be very small, but over a long period of time it’s possible that the newly painted hazardous asteroid’s trajectory could be altered so much that it is moved out of harm’s way.

Obviously, the engineering challenge of making this plan a reality is huge, and there will be some debate over the possibility of making the asteroid threat worse (say if the asteroid trajectory changes in an unpredictable way?), but it’s good that we have a few (theoretical) options at our disposal when it comes to incoming asteroids.

Unfortunately, whether we have 20 years or 20 days notice of an impending asteroid strike, it will likely be mankind’s complacency and lack of investment in space technology that will be our ultimate undoing. Perhaps we need to get hit by a small asteroid before the world’s leaders take note. After all, it’s not a matter of if we get hit by a deadly asteroid, it’s a matter of when.

Source: MIT

Image: Asteroid Apophis and paintballs? Credit: ESA/iStock, edit by Ian O’Neill

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