Deflecting killer asteroids with nuclear weapons has long been the stuff of science fiction. But thanks to an experiment at Sandia National Laboratories, that scenario has taken a step closer to reality.
Led by physicist Nathan Moore, researchers at Sandia in Albuquerque, New Mexico, used a powerful X-ray beam to blast tiny chips of quartz and silica, just as they hope future teams might steer an asteroid off a collision course with Earth.
The X-rays exploded the surface of the chips, releasing a cloud of vapor that propelled them away from the laser at 160 mph (260 km/hr). Computer models suggest this should work at scales far larger than they tested in the lab. While the experiment used chunks of material only half an inch (1.2 cm) across, Moore’s team says their calculations show that the basic idea is powerful enough to successfully deflect asteroids up to 2.7 miles (4.4 km) across, making their research, published today in Nature Physics, a significant step toward practical planetary defense.
Nuclear defense
The solar system is full of rocky space trash, left over from its formation or created by eons of collisions. Chance gravitational encounters can send these asteroids speeding out of the solar system — or into an unsuspecting planet. One such object, some 6 to 9 miles wide (10 to 15 kilometers) wide, probably smashed into Earth 66 million years ago and wiped out the dinosaurs. The question is not whether another large impact will occur, but when.
The effort to prevent such a disaster is termed planetary defense, and it takes many forms. NASA is responsible for leading the detection and tracking of possible impactors. The agency also sent the DART (Double Asteroid Redirection Test) mission to asteroid 65803 Didymos and its small moonlet Dimorphos, to see if hurling a projectile into a space rock might deflect it. (It did.)
But larger asteroids might require multiple impacts, each one moving the asteroid some amount. In that case, an energy-based deflector system starts to appeal.
Enter the nukes.
Yes, just as in the movie Armageddon, scientists believe that nuclear weapons could also be tools to protect Earth from encroaching asteroids. However, detonating a nuclear weapon directly on an asteroid could risk fracturing the asteroid instead of significantly deflecting it, raining many smaller but still deadly meteorites onto Earth.
A leading proposal is to instead set off a nuclear bomb at some distance from the asteroid. Such an explosion is more likely to deflect the asteroid instead of breaking it apart.
But since deploying nuclear weapons in space is a violation of the 1967 Outer Space Treaty — and not to be used lightly in any case — it can be difficult to test this theory.
Asteroid jetpack
Moore and his colleagues turned to Sandia’s Z Pulsed Power Facility, a powerful pulsed energy machine capable of creating conditions as extreme as a large nuclear explosion — albeit on a much smaller scale.
The Z machine — as it’s informally called — is the largest pulsed power machine in the world. It fires electrical pulses 1,000 times stronger than a bolt of lightning, delivering up to 22 megajoules of X-ray energy to test objects. This amount of energy is tiny in the world of nuclear detonations, but more than enough to practice on mini asteroids. Moore’s experiment used two chips — one of quartz and one of fused silica, the latter being a common component in asteroids.
The X-rays themselves imparted some momentum to the chips, but the majority of the push came from a different mechanism: The X-rays heated the surface of the material, causing it to vaporize. The material then expanded away from the surface, much like a rocket or jetpack, shoving the chip in the opposite direction. Scientists observed the same effect when the DART mission crashed into Dimorphos — the flying ejecta propelled the asteroid further than the spacecraft impact itself.
Moore says laboratory experiments are important to understanding how an asteroid might react to a real deflection attempt. Asteroids are notoriously misshapen, odd conglomerates of material — which is hard to model accurately with computers. Running an experiment on increasingly complex samples becomes the easier option.
While the current experiment is a proof of concept with simple chips, he and his colleagues plan to test more realistic and complicated mixtures of iron and nickel. “That’s why it’s so important to have this experiment,” says.
For now, NASA says our skies are clear. Hopefully they’ll remain that way until Moore, NASA, and other groups get us a little closer to answering how to to steer an asteroid.
