It’s been almost 25 years since Bruce Willis, playing the fictional character Harry Stamper in the blockbuster movie, Armageddon, saved Earth from an asteroid careering towards the planet. In true Hollywood fashion, he did this by detonating a nuclear bomb implanted in the asteroid, preventing what scientists call a “mass extinction event”. The whole world cheered (at least in the movie).
The world might be able to cheer for real now. In a study published in Nature Physics, physicists at Sandia National Laboratories in New Mexico, US, say they have simulated a nuclear X-ray pulse directed onto the side of an asteroid to change the trajectory of the asteroid and avoid a collision with the Earth.
How did the experiment work?
In a recent experiment conducted at Sandia National Laboratories, researchers used a Z machine to generate the X-ray pulses. This is one of the world’s most powerful radiation machines that can generate magnetic fields and X-rays.
To generate the X-ray pulse, an intense electrical burst is directed at a pocket of argon gas. This triggers an implosion of the argon gas and turns it into plasma. The plasma emits a powerful surge of X-rays towards the target, effectively mimicking a nuclear detonation in space.
Scientists used an X-ray pulse inside a vacuum to simulate a nuclear explosion on the surface of an asteroid-like rock in space-like conditions. The pulse created a vapour plume which pushed the rock away.
“The vaporised material shoots off one side, pushing the asteroid in the opposite direction,” Dr Nathan Moore, the lead author of the new study, said in a press statement.
In an interview with Space.com, an online publication focused on space exploration and astronomy, Moore said: “You have to concentrate a lot of power, about 80 trillion watts, into a very small space, the size of a pencil lead, and very quickly, about 100 billionths of second, to generate a hot enough argon plasma, several millions of degrees, to make a powerful enough X-ray burst to heat the asteroid material surface to tens of thousands of degrees to give it enough push.”
He also explained that creating an environment that replicates one in which asteroids move freely through space without anchoring the asteroid-like rock used for the experiment was a challenge.
The solution was to use what they called “X-ray scissors”. This involved hanging the rock using extra thin foil wires about one-eighth the thickness of a human hair.
“A key fact was that asteroids in outer space aren’t attached to anything. But in a lab, everything is pulled down by Earth’s gravity, so everything is held in place by its gravitational attachment to something else. This wouldn’t let our mock asteroid move with the freedom of one in outer space. And mechanical attachments would create friction that would perturb the mock asteroid’s motion,” Moore said in a press statement.
This method allowed the scientists to simulate the effects of a nuclear explosion in a controlled environment.
Although only a simulation, the outcome of the experiment suggests that using a nuclear X-ray pulse on an asteroid could potentially change its trajectory enough to prevent a collision with the Earth.
“I knew right away that this was a huge success,” said Moore.
Does a nuclear X-ray pulse have the same effect as a nuclear blast?
There is a significant difference between planting a nuclear bomb on an asteroid and directing a nuclear X-ray pulse to part of an asteroid to nudge it onto a different trajectory.
If a space agency were to successfully detonate a nuclear bomb on an asteroid, scientists have cautioned that the asteroid would be likely to break into smaller chunks, potentially causing multiple asteroid impacts on Earth instead of just one.
Even if the trajectory of the biggest chunk of the asteroid was changed, there would be no guarantee that the other fragments of the asteroid would travel away from Earth.
Using an X-ray pulse, scientists can generate energy to vapourise enough material from the surface of the asteroid to result in a push that would change the trajectory of the asteroid rather than blasting it into smaller fragments.
Have we tried to change the trajectory of an asteroid before?
Changing the trajectory of an asteroid might appear more fiction than science, but in November 2021, the Double Asteroid Redirection Test (DART) mission by NASA crashed a spacecraft into the asteroid Dimorphos and successfully changed the asteroid’s orbital path. Fortunately, the Dimorphos asteroid was no threat to Earth. It was selected to test whether an impact from another object could be a viable method for deflecting an asteroid.
How close do asteroids come to Earth?
Last week, 2024 ON asteroid, a Near-Earth Object (NEO) measuring 290m (950 feet) in length, safely passed Earth at a distance of almost 1 million km (621,000 miles), about 2.5 times the distance between the Earth and the moon.
NEOs are asteroids or comets that are monitored by ground-based and space-based telescopes to identify potentially hazardous objects, especially those that have the potential to impact Earth.
On June 19, 2004, the asteroid 99942 Apophis, appropriately dubbed “God of Destruction”, measuring 370m (1,210 feet) in length, was spotted by astronomers Roy A Tucker, David J Tholen and Fabrizio Bernardi from the Kitt Peak National Observatory in Arizona.
At the time, the scientists predicted that Apophis would eventually hit Earth on April 13, 2029. However, new research suggests that the asteroid will do a close fly-by the same day and is expected to pass about 32,000km (19,800 miles) from Earth, closer than some satellites that orbit the planet.
On February 23, 2012, asteroid Duende, a NEO roughly 30m (98 feet) in diameter, was discovered by astronomers at the La Sagra Observatory in Spain. Duende made a close approach to Earth, passing at about 27,700km (17,200 miles), even closer than Apophis asteroid.
What are the ethical implications of using nuclear energy to divert asteroids?
Although the physicists at Sandia National Laboratories only simulated the equivalent of a nuclear explosion on an asteroid-like material using X-rays, if such a device were to be built, questions about the regulation and ethics of using nuclear power in space would arise.
David Blunt, lecturer in international relations at the University of Sydney and fellow of the Ethics Centre, said: “This is sort of a hypothetical weapon – we don’t know the details of it – but if it has the ability to create a blast radius comparable to an advanced nuclear weapon, then it would fall, basically into the category of a weapon of mass destruction which tends to be weapons that are immensely powerful but also indiscriminate.”
According to Blunt, the closest comparison, albeit imperfect, we have to an industry that would be regulated like this nuclear X-ray device is nuclear power.
“A lot of states are interested in having nuclear energy, but depending on what you do or depending on the reactor, the sort of byproduct of the nuclear waste can be weaponised, whether we’re talking about depleted uranium or radiological devices like dirty bombs or if it’s used to create material for a fission or fusion bomb.”
In addition, a regulatory body that controls who has access to such a device would be required.
Blunt said: “So I would say, if I’m a head of this agency, if we were going to ever use it, you would have to have more than one state, more than one person, that would ensure it could never be directed against the Earth itself.”
At present, there are well-established organisations that are responsible for planetary defence, including the Planetary Defense Coordination Office (PDCO), which operates under NASA, and UN-supported organisations including the International Asteroid Warning Network (IAWN), but none are specifically responsible for the regulation of nuclear energy as it relates to planetary defence.
Some experts would argue the National Nuclear Security Administration (NNSA), part of the US Department of Energy, would be the closest.
