Scientists, as well as Hollywood filmmakers, have long looked to nuclear bombs as a promising form of defense should a massive asteroid appear without warning on a collision course with Earth.
Now researchers at a US government facility have put the idea on a firm footing, showing how such an explosion could save the world in the first comprehensive demonstration of nuclear-backed planetary defense.
Physicists at Sandia National Laboratories, whose primary mission is to ensure the safety and security of the US nuclear arsenal, recorded in nanosecond detail how a tremendous pulse of radiation unleashed by a nuclear explosion hit the side of a nearby asteroid can evaporate.
The event is so violent that it heats the surface to tens of thousands of degrees, producing a rapidly expanding ball of gas capable of pushing the asteroid off course. Do the sums correctly and the shunt should be sufficient to stave off doomsday.
“The vaporized material shoots from one side and pushes the asteroid in the opposite direction,” said Dr. Nathan Moore, first author of the study. “It’s like turning the asteroid into its own rocket.”
Devastating asteroid impacts are rare in Earth’s history, but humans learned the lesson 66m years ago that space rocks can spell catastrophe. The asteroid that ended the reign of the dinosaurs was about 6 miles wide, but much smaller rocks are still dangerous. The 60-foot-wide meteor that exploded over the Russian city of Chelyabinsk in 2013 was injured more than 1,200 people.
Given the existential nature of the threat, researchers are exploring strategies to protect the Earth from massive impacts. In 2022, Nasa’s Dart deliberately probed struck at Dimorphos, a small moon of an asteroid called Didymos. The mission showed that a kinetic impact could protect Earth, but the push had to be given years before the impending impact.
The nuclear option is for larger asteroids, especially when time is short. It doesn’t involve shooting down asteroids or taking Bruce Willis’ approach in the movie Armageddon to drop a bomb into a borehole. More effective is a standing explosion, which vaporizes part of the asteroid’s surface and leaves the rest to Newton’s. third law of motion.
To test the idea, Moore and his colleagues set up an unprecedented experiment that exposed chunks of mock asteroid to intense X-ray pulses similar to those released in nuclear explosions. The pulse first wipes out supports that hold the material in place and then rapidly vaporizes the target surface, creating an expanding gas that sends it flying.
Write in Nature Physicsthe researchers describe how the mock asteroids were subject to gravity once the supports were destroyed, but that they fell less than 2 millionths of a millimeter before the 20 microsecond experiment was over. The chunks of ridiculous asteroid were propelled to nearly 200 mph.
The strategy should work for asteroids up to 2.5 miles wide, the scientists say, but that’s not a hard upper limit. “If there is enough warning time, one can certainly deflect larger asteroids,” Moore said.
Prof Colin Snodgrass on the Dart mission science team at the University of Edinburgh said it was important to understand how to scale the results to full-sized asteroids. The European Space Agency Hera missionlaunching next month should help by exploring the aftermath of Dart’s impact on Dimorphos.
Prof Gareth Collins, a planetary scientist at Imperial College, called Moore’s experiments “spectacular”. “I still have a strong preference for non-nuclear options, especially single or multiple kinetic impactors, as we know they are technologically feasible,” he said. “But for a very large asteroid or a short warning time, this type of approach may be our only option.”
