If a dangerous asteroid heads toward Earth, one way to protect against it could be a nuclear explosion: X-ray radiation would strike one side of the celestial body and slightly shift it off course. However, new computer simulations show that for an irregularly shaped asteroid, the result depends heavily on exactly where the strike lands.
The study was published in the journal Icarus. Scientists led by physicist Nathan Moore of Sandia National Laboratories (USA) irradiated different sides of the same simulated asteroid. It turned out that the momentum transferred and the resulting rotation change depending on the impact point.
In one case, the displacement velocity - that is, the change in linear velocity after the simulated X-ray flash - was 3.9 millimeters per second for a strike at one angle and only 0.8 millimeters per second at another. The difference is almost fivefold. "We expected that aim would matter," Moore said. "What surprised us was how much."
For another asteroid, the change in rotation rate after the strike differed by a factor of 17.
These results emphasize that in a real attempt to deflect an asteroid with a nuclear explosion, knowing its shape and choosing the right side to strike could be critically important.
Previously, most models simplified the task by choosing between a realistic asteroid shape and precise mathematics. Moore's team created a model that accounts for both. "Our new algorithm runs more than 1,600 times faster, and that was the key to the breakthrough," the researcher explained. "Computers simply could not handle the old models."
The simulation uses data from high-detail 3D scans of asteroids obtained by passing spacecraft. The program then calculates how much the explosion would accelerate the asteroid, how quickly it would begin to rotate, and whether its surface would break apart. The last point is especially important: the goal is to push the asteroid, not shatter it into smaller but still dangerous fragments.
So far, the model accounts only for the destruction of surface rock. "We cannot yet accurately predict the destruction of the entire asteroid as a whole," Moore admits. That requires additional research and more advanced tools.
In addition, the calculation requires sufficiently accurate data on the asteroid's shape from all sides, and there may not be time to collect it. Placing an explosive device at the ideal distance on the needed side of an object hurtling through space is also not easy.
Nevertheless, the work reduces the share of guesswork in preventing a catastrophe. "Our study shows how important it is to aim carefully," Moore says. "Pick the right side and you win. Make a mistake and it could be a bad day."