Specialists at Lawrence Livermore National Laboratory (LLNL, USA) are creating three-dimensional computer models to understand how a nuclear explosion near an asteroid could deflect it from Earth or destroy it. The work was published in The Planetary Science Journal.
The asteroid threat differs from many natural disasters: if a dangerous object is spotted in advance, an attempt can be made to avoid a collision. One path is deflection: the asteroid is given a small additional velocity and it passes by Earth with almost no disruption. The other is destruction: the object is deliberately broken up and dispersed so that no fragment poses a serious danger.
In 2022, the US space agency NASA conducted the DART mission (Double Asteroid Redirection Test): the spacecraft deliberately crashed into the moonlet of the asteroid Dimorphos, demonstrating the kinetic method of deflection. The nuclear option is considered a backup emergency method - especially for large objects or when warning time is short, since an explosion can impart far more energy to an asteroid than a spacecraft impact.
The new work used the Spheral code developed at LLNL. It describes in more detail how the asteroid's material behaves when X-ray radiation from the explosion rapidly heats and vaporizes it at the surface. First the approach was validated: more than 1,500 one-dimensional Spheral calculations were compared with results from another laboratory code, Ares. The agreement proved close, which allowed the researchers to move on to more complex three-dimensional scenarios.
The researchers then modeled three cases of destruction of an irregularly shaped asteroid about 160 meters (525 feet) in diameter. The calculations varied the distance to the hypothetical explosion and assumptions about how easily the asteroid's material cracks.
In the longest calculation, about 98% of the asteroid's material received full damage - its ability to maintain integrity was seriously undermined. About 97% of the material was moving faster than the asteroid's escape velocity, that is, fast enough to overcome its gravity; most of the material flew off in opposite directions. This indicates disintegration of the body. In two of the three scenarios, strong signs of destruction appeared.
The results also showed that where exactly the energy is distributed matters. In one case, an explosion farther from the surface delivered less total energy but damaged a larger area because the energy was spread more widely. This does not mean that a distant detonation is always more effective: the optimal option depends on the asteroid's size, shape and composition, and on whether it needs to be deflected or destroyed.
The authors note limitations. The longest calculation ran for 59 days on 1,680 processors but advanced the model by only 145 milliseconds of physical time. Determining the sizes and trajectories of the fragments requires far longer calculations. Reliable destruction requires proving that no remaining fragment exceeds about 10 meters (33 feet) and that the debris disperses rather than reaccumulates. Current models did not run long enough for such a conclusion, although the scale of damage and the motion of material in two cases indicate that breakup had begun.
In the future, the researchers plan to speed up the calculations, increase resolution and model more realistic asteroid structures, including loose "rubble piles." They also intend to compare the models with small-scale laboratory experiments.