For decades, everyone from sci-fi writers to defense specialists and Hollywood directors have hypothesized about how best to save the planet should it ever come face to face with a massive asteroid. Now, they might finally have their answer. According to a new proof-of-concept study published by scientists on Monday, blasting any asteroid out of the sky with a gigantic X-ray beam may be our best bet at saving the human race.
In the study, published in Nature Physics, researchers created and suspended mock asteroids in a lab, before using an X-ray field to vaporize their surfaces and deflect them off course. They say the method could be scaled up for use in future planetary defense missions.
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Faithfully replicating the kilometer-wide asteroids that might endanger Earth should they crashland upon it was always going to be a big ask. So, researchers created two miniature 12mm-wide asteroids for their experiment, both made from forms of the same mineral—silica—that is commonly found in asteroids. One was made of quartz (the hard, crystalline version of silica) and the other of fused silica, where the molecules are arranged more haphazardly.
They hung these pint-sized asteroids in a vacuum using ultra-thin foils of aluminum. “We needed the asteroid to be floating in space; it couldn’t be attached to anything,” explained the study’s lead author Nathan Moore, a researcher at Sandia National Laboratories. “How to do this within a billionth of a second is the challenge. It’s not like you could just drop the asteroids using tweezers.”
With their experiment set up, Moore’s team blasted the mini-asteroid models with an X-ray pulse created by compressing argon gas into a plasma. The pulse obliterated the foils, allowing the team to measure how the asteroid would naturally react.
The photons (small particles of energy) in that pulse were also enough to heat and then vaporize the surface of these faux asteroids. The plume the vaporization created then transferred momentum to the targets and shoved them off course at a speed of around 70 meters per second—1.5 times faster than the fastest baseball pitch.
The researchers also plugged their measurements into a computer to simulate how the technique could work in real life. They calculated that the blast could be scaled up to deflect objects as big as four kilometers in diameter—way more than the one-kilometer asteroids that are most likely to impact Earth.
Instead of an argon plasma, though, a real-world scenario would likely rely on a nuclear bomb detonated from a spacecraft a few kilometers away from the asteroid. That’s more desirable than landing a nuclear bomb—Armageddon-style—on the asteroid’s surface, explained Moore, because there’s a risk the asteroid could fracture with too big an explosion. “There’s a risk you might fracture it and scatter pieces in undesirable directions,” he said.
An X-ray blast might also be preferable to the other major contender for planetary defense: kinetic impact, or—in layman’s terms—ramming the asteroid with a spaceship. In November 2021, NASA showed how this might be possible with its Double Asteroid Redirection Test (DART) mission. The problem is that we’d need ample time—as in decades—to prepare such a mission, and even then it only really works for small or medium objects. “If you have a short warning time or a larger asteroid, you have no choice but to use something like an X-ray.”
Other creative options include strapping fusion rocket engines onto the asteroid to steer it away, sending a swarm of spacecraft to laser it, or using the neutrons from a nuclear explosion to vaporize and push the object off course.
So, an X-ray blast sounds like it may well be the key to mission success, giving humanity its best shot at survival. Even if few movies so far have made it the saving grace of their plots.
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