LLNL Simulations Explore Nuclear Asteroid Defenses

Lawrence Livermore National Laboratory (LLNL) researchers are developing three-dimensional simulations to examine how a nuclear device could be used to deflect or potentially disrupt an asteroid threatening Earth. The work, published recently in The Planetary Science Journal, uses LLNL's Spheral simulation code to more accurately model how an asteroid might respond when X-rays from a nuclear device detonated near its surface rapidly heat and vaporize material.

After validating the approach against established asteroid-deflection models, researchers used Spheral to study three complex disruption scenarios. Unlike many natural disasters, a hazardous asteroid impact could potentially be prevented if the object is detected early enough. One approach is deflection - imparting a small change in velocity that causes the asteroid to miss Earth while largely remaining intact.

Another approach is disruption, in which an asteroid is intentionally fragmented and dispersed so that no remaining piece poses a significant threat to the planet. NASA's Double Asteroid Redirection Test, or DART, demonstrated a kinetic-impact approach to deflection in 2022 by deliberately striking the asteroid moon Dimorphos.

Nuclear mitigation represents an alternative emergency option, particularly for larger objects or scenarios with shorter warning times, because much more energy can be delivered to an asteroid than the kinetic energy of a spacecraft impactor. Two of the simulations showed strong signs of disruption, highlighting how high-fidelity 3D modeling can help researchers better understand how an asteroid could respond to a nuclear mitigation attempt.

"These simulations give us a much more detailed picture of how an asteroid may respond to a nuclear mitigation attempt," said Isaiah Santistevan, who led the study. "Being able to model damage, fracture and material motion in three dimensions is an important step toward improving our ability to evaluate planetary defense options." Graphic image depicts 3D simulation showing, from left, material damage, material velocity and the x-component of velocity.

The simulation shows extensive damage and material moving in opposite directions, signs that the asteroid is breaking apart. (Graphic courtesy of Isaiah Santistevan) Building a 3D modeling capability To test the approach, the team compared more than 1,500 one-dimensional Spheral simulations with asteroid deflection results from LLNL's established Ares simulation code.

The calculations showed close agreement between the two codes, giving researchers confidence to use Spheral for more complex 3D disruption simulations. Spheral is particularly well-suited to modeling problems involving material damage, fracture and fragmentation, Santistevan said.

The researchers then modeled three disruption scenarios involving an irregularly shaped asteroid roughly 160 meters across, varying both the distance of the hypothetical nuclear detonation and assumptions about how easily the asteroid material would fracture. Strong signs of disruption In the longest-running simulation, about 98% of the asteroid material became fully damaged, meaning it had severely lost its ability to remain intact.

The simulation also showed that roughly 97% was moving faster than the asteroid's escape velocity, with the majority of material moving in opposite directions, further indicating that the body was breaking apart. "What's encouraging is that we're seeing the asteroid sustain extensive damage while material is also moving fast enough to escape its gravitational pull," Santistevan said.

"Those are important indicators that the asteroid is in the process of disrupting, and the 3D simulations allow us to examine that process in much greater detail." The results also highlighted the importance of where energy is deposited across an asteroid. In one case, a detonation farther away from the asteroid's surface deposited less total energy but produced more widespread damage because the energy was spread over a larger area.

The finding does not mean a more distant detonation would always be more effective. The optimal approach would depend on factors including an asteroid's size, shape and composition, as well as whether the objective is deflection or disruption. Pushing the limits of simulation The work also highlights the computational challenge of following an asteroid through the full disruption process.

The longest simulation used 1,680 processors for 59 days but advanced the calculation to only 145 milliseconds of physical time. Researchers would need to follow the fragments much longer to determine their eventual size and trajectories, Santistevan said. That longer-term analysis is important because robust disruption requires showing that no remaining fragment is larger than about 10 meters and that the fragments disperse rather than reaccumulate.

The current simulations did not run long enough to explicitly make that determination, but the extent of damage and material motion in two cases strongly suggests they were in the process of disrupting. Future work will focus on accelerating simulation times, improving resolution and modeling more realistic asteroid structures, including loosely bound "rubble-pile" asteroids.

Researchers also plan to compare simulations with small-scale laboratory experiments. The paper, " Nuclear Mitigation of Hypothetical Asteroid Threats in Smoothed Particle Hydrodynamics ," was authored by Isaiah B. Santistevan, Mary T.

Burkey, J. Michael Owen, Kathryn M. Kumamoto, Jason M.

Pearl and Robert A. Managan. /Public Release. This material from the originating organization/author(s) might be of the point-in-time nature, and edited for clarity, style and length.

Mirage.News does not take institutional positions or sides, and all views, positions, and conclusions expressed herein are solely those of the author(s).View in full here .