What If We Only Had Weeks to Stop a Killer Asteroid? Our Best Bet Is Straight Out of Hollywood.

Earth hasn’t seen an impact as intense as the Chicxulub asteroid since the Late Cretaceous. If it had, we might have never existed.

At about 6 to 9 miles across, with explosive force 4.5 billion times greater than the atomic bomb that devastated Hiroshima, this behemoth obliterated 75% of life on the planet, most famously all non-avian dinosaurs. Volcanoes were spewing lava and ash everywhere in its wake. Enormous tsunami waves rose from the oceans. Irreversible climate change followed, and anything that survived in the aftermath barely managed. That was 66 million years ago.

While nothing of that magnitude has happened since, an encore isn’t impossible. Projectiles continue to fly through space at incredible speeds. Some of them follow orbits that may someday bring them far too close to Earth, which is why prevention is being taken seriously. In 2022, NASA’s DART mission successfully deflected the asteroid Didymos by striking its moon Dimorphos, proving that a kinetic impactor could send a space rock out of orbit. Didymos was a viable experimental target because it was small and never a threat. What if something much more menacing came barreling towards us? It would be impractical to launch a swarm of impactors for something the size of Chicxulub. This is why a team of researchers at the Lawrence Livermore National Laboratory (LLNL) ran simulations of an asteroid nuke.

Taking out an impactor with a nuclear detonation was never out of the question. While its effectiveness has been debated, early detection of a monster asteroid followed by physical action could mean the difference between survival and extinction. Headed by physicist Isaiah Santisevan, the LLNL team has been experimenting with scenarios in which larger objects come straight at Earth with unnervingly short warning times. Most meteorites that break into the atmosphere usually burn up before ever hitting the ground. Hypothetically, a gargantuan hunk of rock would have enough mass to stay intact, unless something either managed to deflect the invader or shatter it into pieces small enough to avoid any serious damage. Using a powerful nuke could either bump the approaching asteroid off course or blow it apart.

“An alternative approach is nuclear mitigation, where a nuclear explosive device (NED) is used to deflect or robustly disrupt the asteroid,” Santisevan said in a study recently published in The Planetary Science Journal. “The energy output available from an NED is much higher than a kinetic impactor, enabling larger [velocity] for deflection, or energy for intentional robust disruption at shorter warning times and for larger targets.”

When simulating a nuclear approach, the most common model of NED mitigation is known as a standoff burst. Using this model, the device is detonated at a predetermined height above the surface of the asteroid, at enough of a distance from Earth that neither the planet nor its satellites would face the risk of anything worse than a shower of cosmic dust (if even that). Because most NED energy is generated as x-rays, it ends up in a thin surface layer of the asteroid, vaporizing and eroding it. What has been vaporized will expand until it overcomes the asteroid’s gravity field and is blasted out, with the shift in momentum changing its velocity. That massive release of energy also sends a shock wave through the body of the rock—one extreme enough to fragment an asteroid into literal smithereens.

Santisevan ran simulations in Spheral with virtual asteroids made of different materials. Each would determine how high above an asteroid the nuke would have to be detonated, along with the amount of force needed to dismember the incoming projectile depending on its material composition, mass, and velocity. LLNL’s Ares simulation code was used to predict the results of a deflection. After 1,500 one-dimensional simulations, the researchers leveled up to 3D, modeling nuclear disruptions of an asteroid about 525 feet in diameter, changing detonation distance and fracturing potential with every simulation.

In the longest simulation, the asteroid fell apart, with most of its material streaking through space in the opposite direction. Shards of rock were moving faster than the asteroid’s escape velocity, meaning it was defying gravity. Future research will follow the trajectories of these fragments to find out where they end up.

“These results are a step toward the immensely difficult problem of doing comprehensive nuclear mitigation modeling for planetary defense scenarios,” the researchers said. “High-fidelity simulations as the ones presented here allow us to keep pushing the limits of what is possible.