For the first time, physicists in the US have done lab-based experiments that show how an asteroid could be deflected by powerful bursts of X-rays. With the help of the world’s largest high frequency electromagnetic wave generator , Nathan Moore and colleagues at Sandia National Laboratories showed how an asteroid-mimicking target could be freely suspended in space while being accelerated by ultra-short X-ray bursts.
While most asteroid impacts occur far from populated areas, they still hold the potential to cause devastation. In 2013, for example, over 1600 people were injured when a meteor exploded above the Russian city of Chelyabinsk. To better defend ourselves against these threats, planetary scientists have investigated how the paths of asteroids could be deflected before they reach Earth.
In 2022, NASA successfully demonstrated a small deflection with the DART mission, which sent a spacecraft to collide with the rocky asteroid Dimorphos at a speed of 24,000 km/h. After the impact, the period of Dimorphos’ orbit around the larger asteroid, Didymos, shortened by some 33 min.
However, this approach would not be sufficient to deflect larger objects such as the famous Chicxulub asteroid. This was roughly 10 km in diameter and triggered a mass extinction event when it impacted Earth about 66 million years ago.
Powerful X-ray burst
Fortunately, as Moore explains, there is an alternative approach to a DART-like impact. “It’s been known for decades that the only way to prevent the largest asteroids from hitting the earth is to use a powerful X-ray burst from a nuclear device,” he says. “But there has never been a safe way to test that idea. Nor would testing in space be practical.”
So far, X-ray deflection techniques have only been explored in computer simulations. But now, Moore’s team has tested a much smaller scale version of a deflection in the lab.
To generate energetic bursts of X-rays, the team used a powerful facility at Sandia National Laboratories called the Z Pulsed Power Facility – or Z Machine. Currently the largest pulsed power facility in the world, the Z Machine is essentially a giant battery that releases vast amounts of stored electrical energy in powerful, ultra-short pulses, funnelled down to a centimetre-sized target.
Few millionths of a second
In this case, the researchers used the Z Machine to compress a cylinder of argon gas into a hot, dense plasma. Afterwards, the plasma radiated X-rays in nanosecond pulses, which were fired at mock asteroid targets made from discs of fused silica. Using an optical setup behind the target, the team could measure the deflection of the targets.
“These ‘practice missions’ are miniaturized – our mock asteroids are only roughly a centimetre in size – and the flight is short-lived – just a few millionths of a second,” Moore explains. “But that’s just enough to let us test the deflection models accurately.”
Because the experiment was done here on Earth, rather than in space, the team also had to ensure that the targets were in freefall when struck by the X-rays. This was done by detaching the mock asteroid from a holder about a nanosecond before it was struck.
X-ray scissors
They achieved this by suspending the sample from a support made from thin metal foil, itself attached to a cylindrical fixture. To detach the sample, they used a technique Moore calls “X-ray scissors”, which almost instantly cut the sample away from the cylindrical fixture.
When illuminated by the X-ray burst, the supporting foil rapidly heated up and vaporized, well before the motion of the deflecting target could be affected by the fixture. For a brief moment, this left the target in freefall.
In the team’s initial experiments, the X-ray scissors worked just as they intended. Simultaneously, the X-ray pulse vaporized the target surface and deflected what remained at velocities close to 70 m/s.
The team hopes that its success will be a first step towards measuring how real asteroid materials are vaporized and deflected by more powerful X-ray bursts. This could lead to the development of a vital new line of defence against devastating asteroid impacts.
“Developing a scientific understanding of how different asteroid materials will respond is critically important for designing an intercept mission and being confident that mission would work,” Moore says. “You don’t want to take chances on the next big impact.”
The research is described in Nature Physics.
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