Asteroid shape dictates where nuclear X-rays must strike for deflection

A team led by Nathan Moore at Sandia National Laboratories ran new simulations showing that the geometry of an asteroid controls where X-rays from a nuclear burst need to hit to deflect the object, according to their study published in Icarus in 2026.

One test run showed a nearly fivefold difference in momentum transfer: one irradiation angle shifted the asteroid’s linear speed by 3.9 millimeters per second, while another angle moved it by only 0.8 millimeters per second. When researchers irradiated a different modeled asteroid from another face, its spin rate changed by a factor of 17 compared with the first angle. Moore said the team expected aim to matter, but the size of the effect surprised him. “Pick the right side and you win,” Moore said.

Moore’s team combined two Sandia simulation codes to handle realistic shapes and high-fidelity physics together. One code, ALEGRA, typically simulates fast high-energy tests like magnetically imploding wires on Sandia’s Z machine. The other, SPARTA, handles weak slowly evolving forces such as solar-wind drag on satellites. The combined code runs more than 1,600 times faster than older models, and Moore said that speed gain made the work possible because older computers could not manage the calculations.

The project started after a Z machine experiment demonstrated that X-rays could push a small sample of asteroid material, leading Moore to scale the math up to a full asteroid. Moore said the idea came after a colleague’s work on outgassing in space (the release of gas) gave him an aha moment to drop spherical approximations. Scientists often simplified the math by treating asteroids as spheres, but Moore said spherical asteroids do not exist because real bodies have uneven, lumpy shapes. Researchers can feed high-resolution 3D flyby imagery into the tool and adjust the blast’s size, standoff distance (the distance from the blast to the asteroid’s surface) and the face of the asteroid that receives the X-rays.

The software produces a heat map of surface vaporization and calculates the push on the asteroid, its spin rate and how much of the surface might fracture, with developers aiming to push an asteroid intact rather than fragment it into smaller potentially deadly pieces. For now, the model only tracks breakup of surface rocks and cannot accurately predict whether the whole asteroid body will break apart. Moore said reaching full-body breakup prediction will take more research and investment because X-ray effects interact in complicated ways.

Planners would need accurate shape data from every angle, which might not be available in time, and placing an explosive at the right distance is difficult. Moore described a theoretical workflow in which operators upload asteroid data, calculate the best explosive yield, distance and direction, and then carry out the blast, though he warned that complete shape data might not arrive in time. Sandia’s Laboratory Directed Research and Development program funded the research.

Separately, Lawrence Livermore National Laboratory researchers modeled a 1-megaton nuclear blast a few meters from an asteroid shaped like Bennu and measuring 160 meters across, with about 30.8 percent porosity and a mass of roughly 3.6 billion kilograms, to study how X-ray heating causes fractures. A nuclear weapon releases roughly 70 percent to 80 percent of its energy as X-rays. “These X-rays deposit energy in a thin surface layer of the asteroid, driving vaporization and ablation,” Lawrence Livermore National Laboratory researchers said.

In the longest Livermore run, 98.2 percent of the material was fully damaged after 145 milliseconds, and roughly 97 percent traveled faster than escape velocity, or the speed needed to escape the asteroid’s gravity. A blast 25 meters above the surface deposited 30 kilotons compared with 55.4 kilotons at 10 meters, yet caused broader damage because the X-rays covered a wider area. Using fracture data from the Aba Panu meteorite made cracks harder to spread: 34.2 percent was fully damaged after 34 milliseconds, versus 60.2 percent using Chelyabinsk parameters.

Livermore researchers cannot yet say whether leftover fragments would fly apart or come back together, since the simulations covered only fractions of a second. LLNL checked Spheral against its Ares code using more than 1,500 one-dimensional comparisons, with close agreement and a standard deviation of 0.8 percent in blow-off momentum. Spheral missed some of the fastest ejecta, so reported velocity changes may be conservative, and limited resolution can overestimate the amount of damaged material. The team said experiments at the National Ignition Facility, OMEGA and Sandia’s Z machine could help improve models of X-ray heating and material loss.

Livermore ran three disruption scenarios using an irregular asteroid about 160 meters across, changing the detonation distance and assumptions about how the material would break. The group published its Spheral modeling work in The Planetary Science Journal. “These simulations give us a much more detailed picture of how an asteroid may respond to a nuclear mitigation attempt,” Isaiah Santistevan said. The paper’s authors were Isaiah B. Santistevan, Mary T. Burkey, J. Michael Owen, Kathryn M. Kumamoto, Jason M. Pearl and Robert A. Managan.

Santistevan said Spheral is particularly well suited to modeling material damage, fracture and fragmentation in three dimensions, and called nuclear mitigation an alternative emergency option for larger objects or shorter warning times because it delivers much more energy than a kinetic impactor. LLNL said the best nuclear approach depends on an asteroid’s size, shape and composition and on whether the goal is deflection or disruption. A more distant detonation is not always better. LLNL plans future work to speed up simulations, improve resolution, model rubble-pile asteroids and compare results with small-scale laboratory experiments.

ESA said NASA’s DART spacecraft hit Dimorphos on Sept. 26, 2022, at about 6.1 kilometers per second, cutting Dimorphos’s orbital period around Didymos by roughly 33 minutes. ESA’s Hera spacecraft captured its first clear view of Didymos and Dimorphos as separate objects on Oct. 18, 2026, while about 1,280 kilometers from the targets. “With this image, the smaller Dimorphos asteroid becomes visible for the first time,” Michael Kueppers said.

ESA said Hera reduced its speed relative to the asteroids to 20 meters per second after two thruster firings in October separated by one week. Dimorphos measures about 151 meters across, comparable to the Great Pyramid of Giza, while Didymos is approximately 780 meters in diameter, slightly smaller than the Burj Khalifa. ESA said Dimorphos travels around Didymos at an average separation of 1.15 kilometers at approximately 18 centimeters per second.

Hera will unveil the first detailed images of Dimorphos on Nov. 25, 2026, and will release two shoebox-sized CubeSats for closer observations, with landing operations expected eventually. Researchers still do not know whether DART left a crater on Dimorphos or altered its shape. ESA said the orbital change was substantially greater than computer simulations predicted, and ESA said researchers need more precise measurements of Dimorphos’s composition, internal structure and mass to understand why the collision was so effective.

ESA said Hera will use scientific instruments to examine the asteroid and surroundings, and ESA expects the investigation to eventually include landing operations. ESA said the Hera Space Companion is an interactive communication platform connected to the mission, designed to make ESA’s first planetary defense mission accessible to the public.