Livermore Simulates 1-Megaton Blast Breaking Up 160-Meter Asteroid

Q: Why might detonating a nuclear bomb farther away from a doomsday asteroid actually cause more destruction than a direct hit?

A nuclear blast set a short distance away can sometimes do more damage because, in space, the main destructive force is not a shockwave but X-rays. Those X-rays spread out over the asteroid’s surface, rapidly heating a thin outer layer, vaporizing material, and blasting it outward. That escaping material acts like rocket exhaust, adding recoil and helping fracture the body. A direct hit or very close detonation concentrates energy on a smaller area. A slightly farther “stand-off” burst can illuminate more of the asteroid at once, much like moving a flashlight back broadens the beam. In the Lawrence Livermore simulations, a detonation 25 meters from a Bennu-like asteroid sometimes produced broader surface damage than one just 10 meters away, even though less total energy reached the rock. That wider X-ray coverage matters because it can create more uniform ablation across the surface and drive shock waves deeper into the asteroid’s interior. The study found those X-ray-driven internal shocks could crack the object from within, increasing the odds of disruption rather than just scorching one side. The finding does not mean “farther is always better.” The effect depends on the asteroid’s size, shape, porosity, composition, and internal strength, as well as warning time. The simulations also covered only the first 145 milliseconds, so scientists still do not know whether the fragments would disperse safely, remain dangerous, or partly reassemble under gravity.

3 articles · Updated · ScienceAlert · Aug 18

A Lawrence Livermore team found a 1-megaton nuclear detonation near a 160-meter “city killer” asteroid could likely disrupt it in two of three simulated scenarios.
X-rays—not a vacuum shockwave—did the work, vaporizing a thin surface layer, ejecting material and changing momentum while also driving fractures through the rock.
At 10 meters, 98.2% of the asteroid was fully damaged and about 97% of material exceeded escape velocity; at 25 meters, damage spread faster early on because a wider area was irradiated.
The simulations tracked only 145 milliseconds of breakup and took 59 days on 1,680 processors, leaving the long-term fate of the fragments unresolved.
The study, published in The Planetary Science Journal, frames nuclear standoff blasts as a possible last-resort planetary defense option when an asteroid is too large or detected too late to deflect.