Study Models How a Nuclear Strike Could Deflect an Asteroid on Short Notice

A new study from researchers at the China Academy of Launch Vehicle Technology, published in the journal Space: Science & Technology, models how a nuclear detonation could deflect an asteroid discovered too late for other defenses — a scenario in which warning time between discovery and impact could be as short as a few days.

As of July 2024, 10,933 of the 35,269 known near-Earth asteroids had diameters larger than 140 meters (460 feet); an object of that size on a collision course could cause continent-wide or even global devastation, though none of the currently known asteroids are on such a path. The researchers modeled two approaches to a short-notice nuclear response. The first, simplest option is to fly a nuclear weapon into the asteroid and detonate it with precise timing to knock it off course — but this makes it hard to choose an ideal detonation site, transfers relatively little of the blast's energy to the asteroid, and requires the warhead to survive high-speed debris impacts and detonate with microsecond precision.

The second approach builds on the Double Asteroid Redirection Test (DART) mission, which shifted a non-threatening asteroid's orbit by striking it with a kinetic impactor. On short notice, however, a kinetic impact alone cannot transfer enough energy to be effective, so the new study proposes first firing a "1+1" tandem impactor — two projectiles striking the same spot in sequence — to excavate a crater tens of meters across, then detonating a nuclear device inside that pit.

In simulations of a 1-kilometer-diameter asteroid, detonating a 3-megaton nuclear device on the asteroid's surface changed its velocity by just 9.2 centimeters per second, but detonating the same device inside a 30-meter pre-excavated crater increased the velocity change to more than 30 centimeters per second — over three times as much. The researchers modeled the asteroids as solid basalt, though most hazardous asteroids are thought to be loosely bound "rubble piles," so it remains unclear whether the results would hold for that more likely case.