Sandia National Laboratories physicist Nathan Moore and nine co-authors ran computer simulations of an X-ray pulse striking lumpy, realistically shaped asteroids and found that the side taking the hit changes the outcome dramatically. For one simulated asteroid, the same blast altered the rock’s speed by 3.9 millimeters per second from one direction and only 0.8 millimeters per second from another. The gap works out to a nearly fivefold difference, produced by aim alone.
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A second simulated asteroid showed a wider spread still. Depending on the direction of the radiation, the change in that object’s spin rate differed by a factor of 17, so one approach angle could leave a rock tumbling very differently from another.
ALEGRA, SPARTA and a lumpy-rock algorithm
The work appears in the journal Icarus, in a paper on computing vapor ejecta over asteroid geometries during pulsed energy deflection. According to the Sandia news release distributed through EurekAlert, the team joined two existing Sandia codes: ALEGRA, normally used for fast, high-energy experiments such as the imploding wires on the Z machine, and SPARTA, a direct simulation Monte Carlo code usually applied to weak, slowly evolving forces like satellite drag. Moore said the point was to get away from spheres, because spherical asteroids do not exist. The models are built from three-dimensional images captured during spacecraft flybys, and the new algorithm runs more than 1,600 times faster than earlier approaches, as ScienceDaily’s account of the research relays from Moore. The other authors are Michael Gallis, D. Gregory Tipton, Zakari Eckert, Timothy Koehler, Kevin Long, Joel Clemmer, Kyle Cochrane, Brian Franke and Mekiel Olguin.
For each run the software varies the strength of the blast, its distance from the surface and its direction. It then draws a heat map of how much of the surface vaporizes and, from that map, estimates the push the asteroid receives, the change in its rotation and the damage to surface rock. In this style of deflection the vaporized material streaming off the surface supplies the shove, so the arrangement of bumps and hollows that face the burst matters a great deal. A faster code lets analysts sweep many blast directions and distances rather than wait on a single heavy run. Sandia published its original release on Nov. 3, and the paper itself came out in Icarus on Oct. 24.
From the Z machine to NASA’s DART impact
Sandia has been working this problem from the laboratory side for some time. An earlier experiment on its Z machine was the first to show that X-rays could deflect a small piece of asteroid material, according to the ScienceDaily summary of the new study. The only full-scale test so far used a very different method. NASA’s DART spacecraft struck the asteroid moonlet Dimorphos on Sept. 26, 2022, and NASA reported that the moonlet’s orbit around Didymos shortened by about 32 minutes, more than 25 times the agency’s minimum success threshold of 73 seconds.
NASA’s later analysis found that Dimorphos kept losing rocky material to space in the weeks after the collision, and its orbital period continued to shrink. The study put the drop in its mean orbital distance from Didymos at about 120 feet (37 meters), from roughly 3,900 feet to 3,780 feet. Ejecta behavior of that kind belongs to the same family of physics that Sandia’s code tracks, though a spacecraft impact and an X-ray flash get there by different routes. Nancy Chabot, the DART coordination lead at the Johns Hopkins Applied Physics Laboratory, said when the first result was announced that the mission had produced fascinating data about asteroid properties.
Limits Moore’s team acknowledges
Moore was candid about what the model cannot do. It considers only the breakup of rock on the surface, and he said it cannot yet predict breakup of the entire asteroid body accurately. An intense X-ray burst sets off many physical effects that influence one another, which makes any precise prediction hard. His practical summary of the aiming result: choose the right side and the deflection works, guess wrong and it could be a bad day. He added that the team expected aim to matter and was surprised by how much.
The software also needs reasonably accurate shape information from every direction, and an asteroid discovered late might leave no time to gather it. Placing a nuclear device at the right position relative to a moving asteroid would demand extraordinary precision as well. ScienceDaily describes the study as guidance on blast direction for planetary defense, not a ready-to-use mission plan.
The research was funded through Sandia’s Laboratory Directed Research and Development program. What remains open is how a planner would pick a side to hit when the shape data are incomplete, since the 3.9 and 0.8 millimeter-per-second figures come from a single simulated rock and the factor-of-17 spin swing from another, each with its geometry fully known.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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