Paris: Humanity could use a nuclear bomb to deflect a massive, life-threatening asteroid hurtling towards Earth in the future, according to scientists who tested the theory in the laboratory by blasting X-rays at a marble-sized "mock asteroid."
The biggest real-life test of our planetary defences was carried out in 2022 when Nasa's fridge-sized DART spacecraft smashed into a 160-metre-wide asteroid, successfully knocking it well off course.
But for bigger asteroids, merely crashing spaceships into them will probably not do the trick.
When the roughly 10-km-wide Chicxulub asteroid struck the Yucatan Peninsula around 66 million years ago, it is believed to have plunged Earth into darkness, sent kilometres-high tsunamis rippling around the globe and killed three-quarters of all life — including wiping out the dinosaurs.
We humans are hoping to avoid a similar fate.
There is no current threat looming, but scientists have been working on how to stave off any big asteroids that could come our way in the future.
A leading theory has been to blow them up with a nuclear bomb — a last-ditch plan famously depicted in the 1998 sci-fi action movie Armageddon.
In the movie, Bruce Willis and a plucky team of drillers save Earth from an asteroid 1,000 km wide — roughly the size of Texas.
For a proof-of-concept study published in the journal Nature Physics this week, a team of US scientists worked on a much smaller scale, taking aim at a mock asteroid just 12 millimetres (half an inch) wide.
To test whether the theory would work, they used what was billed as the world's largest X-ray machine at Sandia National Laboratories in Albuquerque, New Mexico.
The machine is capable of generating "the brightest flash of X-rays in the world using 80 trillion watts of electricity," Sandia's Nathan Moore, the lead study author, said.
Much of the energy created by a nuclear explosion is in the form of X-rays. Since there is no air in space, there would be no shockwave or fireball. But the X-rays still pack a powerful punch.
For the lab experiment, the X-rays easily vaporised the surface of the mock asteroid.
The vaporising material then propelled the mock asteroid in the opposite direction, so that it effectively "turned into a rocket engine," Moore said.
It reached speeds of 250 km an hour, "about as fast as a high-speed train," he added.
The test marked the first time that predictions about how X-rays would affect an asteroid had been confirmed, Moore said. "It really proves this concept could work."
The scientists used modelling to scale up their experiment, estimating that X-rays from a nuclear blast could deflect an asteroid up to 4 km wide — if given enough advanced notice.
The biggest asteroids are the easiest to detect ahead of time, so "this approach could be quite viable" even for asteroids the size of the dinosaur-killing Chicxulub, Moore said.
The experiment was based on using a one-megaton nuclear weapon. The largest ever detonated was the 50-megaton Soviet Tsar Bomba.
If there were to be a planet-saving mission in the future, the nuclear bomb would need to be placed within a few kilometres of the asteroid — and millions of kilometres away from Earth, Moore said.
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