Pieces of celestial objects too small to affect the Earth frequently enter the atmosphere, with a few even reaching the ground. Events where such collisions have any substantial impact, though, are rarer. The last time something fairly large entered the atmosphere was over ten years ago over the Russian city of Chelyabinsk: a piece of an asteroid roughly ‘the size of a small building’ disintegrated about 20km over Chelyabinsk, causing several pieces of meteorite to be showered all over the area.
However, the prospect of a much larger asteroid, one that can create serious consequences for life on Earth, is only small not absent. The Chelyabinsk event saw 1,600 injured. The most famous asteroid to have hit the earth is the Chicxulub which, about 66 million years ago, triggered a mass extinction event that likely saw dinosaurs wiped out. Chicxulub is estimated to have been about 10km in diameter.
Deep impact
The question then is how does one deal with an incoming asteroid? Our immediate response may be that we could force an explosion or collision with another obstacle that would divert the path of the asteroid wither by swaying it entirely or simply changing its orbit to an extent where it no longer poses a threat to life on Earth. Hollywood has explored this idea more than once. NASA too did the same, although on a much smaller scale, when it caused a spacecraft to collide with an asteroid at 24,000 km/h, inducing a 33 min delay in the asteroid’s orbital motion. Called DART (Double Asteroid Redirection Test) the 2022 activity was hailed by NASA as “the world's first demonstration of asteroid deflection technology”.
Unfortunately it has long been known that while such techniques may work for smaller astroids, such as Dimorphos against which NASA conducted the DART experiment, larger asteroids the size of small cities might not budge. For such cases we would need extremely powerful, high-frequency X-ray bursts.
Redirection simulations
Why do X-rays work? Put simply, X-ray bursts are akin to nuclear explosions in that a sufficiently strong, sufficiently quick series of bursts can vaporise layers of an asteroid’s surface, changing its mass and—through impulsive force—shifting its trajectory.
While strategies to defend against asteroids are being worked out quite regularly in physics, the real question has been how they can be tested. We neither have a high frequency of asteroids flying about in our immediate neighbourhood nor a device that can generate X-ray pulses that are large enough, nor (perhaps) the money to fund such undertakings routinely. Until recently these scenarios were tested using computer simulations.
While simulations will likely remain the starting point for all future endeavours, for the first time this week physicists have been able to demonstrate their approach in a physical, albeit miniature, ‘live action’ setting.
The z-pulse experiment
At Sandia National Labs in Albuquerque, New Mexico, is what is called the “Z machine” or “Z“ or, formally, the “Z pulsed power facility”. It is the largest pulsed power facility in the world used to test materials in extreme temperature and pressure conditions. In short, it is an electromagnetic pulse generator (think of a power surge at home) but one that is capable of producing the largest electromagnetic surges humanly capable today.
In their paper published in Nature, the physicists describe how, to replicate space, they placed tiny particles in free-fall and then used a series of pulses from Z to deflect them. Each run of the experiment took no more than a few microseconds.
The particles were about a centimetre in size, made of fused Silica, and were placed in free fall before a set-up of optical observation equipment used to record and measure their deflections. The miniature practice missions were a success, paving the way for building larger EMP equipment for planetary defence.
As with all physics, such miniature experimental set-ups are not reasonably close to a realistic scenario and not simply an overly idealised case, which makes them all the more meaningful for translating into real-life asteroid defence technologies in the coming years. The next step is to conduct the experiment with “asteroids” made of other materials to ensure the technique holds up, or to assess if variations on the theme are necessary for practical applications.
