Where you hit an asteroid may matter as much as how hard you hit it — at least in the computer. New computer simulations from Sandia National Laboratories in Albuquerque, New Mexico, found that for one modeled asteroid, the change in its spin after an X-ray burst varied by a factor of 17 depending on which side was struck.

For another simulated asteroid, the push away from its path was 3.9 millimeters per second when irradiated from one direction and just 0.8 millimeters per second from another, a nearly fivefold difference. The study appears in the journal Icarus.

"We expected aim to matter," said lead author Nathan Moore, a Sandia physicist, according to ScienceDaily. "What surprised us was how much."

The finding matters for planetary defense planning. If a real threat were ever found, a deflection that sends a space rock spinning unpredictably or nudges it far less than intended could waste precious warning time. The work suggests detailed knowledge of an asteroid's shape would be essential before any such mission.

Vaporized Rock as a Rocket Engine

The concept being modeled uses a burst of X-rays, such as those released by a nuclear device detonated near an asteroid rather than on it. In the vacuum of space, there is no shockwave or fireball. Instead, the X-rays flash-heat a thin layer of surface rock, which vaporizes and blasts away, pushing the asteroid in the opposite direction like a brief rocket engine.

Moore's team demonstrated the principle in 2024. At Sandia's Z machine, a powerful pulsed-power facility, they used X-rays to push free-floating mock asteroids of quartz and fused silica about the width of a fingertip, Sandia reported. Those results, published in Nature Physics, were the first experimental confirmation that X-rays could deflect asteroid material.

Scaling that up to a real asteroid was the harder problem. Most earlier models treated asteroids as smooth spheres, which made the math easier but ignored the ridges, depressions, and lopsided shapes that real asteroids show in spacecraft images.

Numbers That Swing With the Angle

The new model combines two Sandia computer codes. ALEGRA is normally used for fast, high-energy events, while SPARTA is a direct simulation Monte Carlo code usually applied to slowly evolving, weak forces such as gas flows. Together they can track how vapor leaves an irregular surface.

The model takes in 3D shape data from spacecraft flybys, then lets researchers adjust the blast's strength, distance and direction. It outputs a heat map of vaporized surface material, the resulting push and change in rotation, and the extent of surface damage.

Speed made the study possible. "Our new algorithm is over 1,600 times faster, which was critical to this breakthrough," Moore said, according to Newswise.

The results show why shape matters. A burst hitting a broad, flat face can send vapor off in one strong direction, while hitting a ridge or a hollow can scatter the push, change how much rock vaporizes, and add torque that alters the spin. Moore summarized the lesson bluntly, saying picking the right side wins, while guessing wrong could mean a bad day.

Shape Data Before Any Mission

The practical takeaway is that reconnaissance comes first. Accurate predictions require reasonably detailed shape information from every direction, the researchers said. That could be a serious problem for an asteroid discovered late, when there may be no time to send a scout spacecraft for a close look.

This links the study to missions already underway. NASA's DART spacecraft struck the asteroid moonlet Dimorphos in 2022 to test the kinetic impactor approach, and the European Space Agency's Hera mission is now arriving to measure the aftermath. Those missions show how much can be learned when a target is mapped in detail, which is exactly the information Sandia's model needs.

The research was funded by Sandia's Laboratory Directed Research and Development program. Sandia is a Department of Energy national laboratory, and the study's co-authors include Michael Gallis, Gregory Tipton, and seven other Sandia researchers.

The approach is also meant to complement, not replace, other options. A kinetic impactor like DART works best with years of warning, while an X-ray burst could deliver a larger push in a single event. In both cases, planners would want to know how a specific asteroid would react before committing to a single attempt.

Boundaries of the Model

The study is a peer-reviewed computer modeling effort, not a test on a real asteroid. Its biggest limit is that it only accounts for the breakup of surface rock. Moore said the model currently considers only the breakup of rocks on the surface, meaning it cannot yet predict whether a blast would fracture the whole asteroid. That matters because many asteroids are thought to be loose rubble piles held together by weak gravity, which could respond very differently to a sudden jolt.

Other uncertainties are large — and some are not computational at all. An X-ray burst would trigger many interacting effects that make real-world behavior hard to predict, and delivering and positioning a device with the required precision would be extremely difficult. The results apply to the shapes modeled, and other asteroids could respond differently.

There is no known asteroid on course to strike Earth, and nothing in this study changes that. For the public, the result is a reminder that planetary defense depends on finding hazardous objects early and studying them closely, so that any response can be chosen with good information rather than a guess.

The bottom line is that aim can swing an asteroid's deflection several-fold and its spin change 17-fold in these simulations. Better shape data and models that capture whole-body breakup are the next steps before the approach could inform a real mission.

What Readers Want to Know

What did the Sandia study find?

Simulations showed that the direction of an X-ray burst changed one asteroid's push nearly fivefold and another's spin change by a factor of 17.

How would X-rays move an asteroid?

They would vaporize a thin layer of surface rock, and the escaping vapor would push the asteroid in the opposite direction.

Is any asteroid currently threatening Earth?

No. There is no known asteroid on course to hit Earth. The study is preparation for a possible future threat.

What are the model's limits?

It only covers breakup of surface rock, not the whole asteroid, and it requires detailed shape data from every direction.

Why is shape data so important?

Ridges, hollows, and lopsided forms change how vapor escapes, which changes both the push and the spin.

How does this relate to NASA's DART mission?

DART tested a different method, crashing a spacecraft into an asteroid. Both approaches depend on knowing the target's shape and makeup in detail.