Nuclear Blast Could Deflect Asteroids, but Aim Matters Greatly

A new study indicates that the aim of a nuclear X-ray burst could determine whether a threatening asteroid is pushed away safely. According to ScienceDaily, the research was led by Nathan Moore, a physicist at Sandia National Laboratories, and appeared in the journal Icarus. Its central finding is that the direction of the burst can lead to strikingly different outcomes, even when the asteroid being targeted stays exactly the same.

In one simulation, the forward speed of the asteroid shifted by 3.9 millimeters per second when radiation arrived from one side. From another side, the shift was just 0.8 millimeters per second. Put simply, the gap is close to fivefold in terms of deflection velocity, which describes how much the forward motion changes because of the burst. Moore said his team had anticipated that aim would be important, yet the size of the effect caught them off guard.

Rotation was affected even more strongly. In a separate simulated asteroid, the spin response changed by a multiple of 17 based on which way the X-rays reached it. The authors suggest that knowing an asteroid’s form, and choosing carefully where to point a blast, may be central to defending Earth from a future strike.

A faster way to model rough shapes

Older computer tools forced a compromise. Scientists generally had to pick between capturing an irregular body accurately and running thorough physics calculations. Doing both at once required more computing capacity than was realistic.

According to the report, the new approach gets around this problem. Researchers can examine lifelike shapes and still calculate the response to an X-ray burst with the necessary accuracy. Moore described the algorithm as more than 1,600 times quicker, a speed gain he called essential to the result. He added that older machines simply could not manage the workload.

The project grew out of an earlier test on Sandia’s Z machine. That test was the first proof that radiation of this kind can push a tiny fragment of asteroid material off course. The next question was how the same process would play out for an entire asteroid. Many studies have simplified the problem by modeling asteroids as spheres. That approach is easier mathematically, yet it ignores ridges, hollows and rough terrain that real rocks often have.

The new model blends two simulation codes that Sandia already uses for unrelated problems. ALEGRA is typically applied to rapid, high-energy events. SPARTA, a direct simulation Monte Carlo program, usually handles gentler forces that act slowly over time. Moore said the breakthrough lay in working out how to link these two methods.

What the software can and cannot show

Users can rebuild an asteroid from detailed three-dimensional images gathered during spacecraft flybys. They can then vary the strength of the explosion, how far it is from the rock and the angle the radiation comes from. The program estimates how much surface material would turn to vapor, the resulting push, the change in spin and the amount of surface damage. It presents vaporization as a heat map.

This matters because an ideal defense mission would alter an asteroid’s path without shattering it into several hazardous pieces. Several smaller fragments could still reach Earth. The model, however, has clear limits. Moore said it currently accounts only for rock breaking apart at the surface. The team cannot yet forecast accurately how the whole body would break up.

More work, funding and stronger computing tools would be needed to close that gap. An intense X-ray pulse can set off many physical effects that interact with one another, and tracking all of them makes precise prediction very difficult.

Obstacles to a real mission

Moore said the study offers practical direction for planners, though a real mission would be hard to carry out. The software depends on reasonably accurate shape data viewed from many directions. If a rock were spotted heading toward our planet, the time available to gather such observations could be too short.

Getting a nuclear device to the correct spot relative to a fast-moving object would also require remarkable precision. Still, the team believes better simulations could shrink the uncertainty around this defense option. Moore described the progress as an encouraging step toward giving humanity a better chance to prevent a devastating impact.

Frequently asked questions

Sources

• ScienceDaily: A nuclear blast could save Earth from an asteroid, but there's a catch

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