Recent demonstration missions such as NASA s Double Asteroid Redirection Test, which altered the orbit of the small asteroid Dimorphos in 2022, have proven that it is possible to deflect a potentially hazardous object by imparting momentum. To predict the outcome of such interventions with confidence, however, scientists need to understand how real asteroid materials respond to extremely rapid and intense energy deposition instead of the slow loading conditions typically used in conventional laboratory tests.

In the new study, an international team including Oxford researchers used CERN s High Radiation to Materials (HiRadMat) facility to expose a sample of the Campo del Cielo iron meteorite to highly energetic proton beams with energies of 440 GeV. The meteorite served as a proxy for metal rich asteroids that contain significant amounts of iron and nickel. By using this accelerator based approach, the team was able to reproduce the kind of rapid internal heating and stress buildup that would occur if an asteroid were struck by a high energy beam or projectile.

The experiment was designed to be non destructive so that the evolution of the material could be followed continuously. The researchers employed laser Doppler vibrometry, a technique that uses laser light to measure extremely small vibrations at the material surface, to monitor how stress waves propagated through the meteorite during and after irradiation. This allowed them to track stress, strain, and deformation in real time rather than relying solely on before and after inspection.

The measurements revealed that the Campo del Cielo sample was able to absorb significantly more energy than predicted by standard material strength models without fragmenting. Instead of failing catastrophically, the meteorite exhibited behavior more typical of a complex composite in which internal structure redistributes stress in non intuitive ways. The response suggested that, under rapid loading, heterogeneous meteorite material can reorganize and strengthen as energy is deposited.

One of the most striking findings was the observation of strain rate dependent damping. The faster the meteorite was stressed, the more effectively it dissipated energy through its internal microstructure. This means that at the very high rates associated with an impact or beam interaction, asteroid material may become tougher rather than weaker, in contrast to expectations based on slower mechanical tests.

These results help explain a long standing discrepancy between the relatively high strengths measured for meteorite samples in the laboratory and the lower strengths inferred from how meteoroids break up in Earth s atmosphere. The new data show that the way stress redistributes through the complex internal structure of meteorites can lead to very different behavior depending on how quickly the load is applied. Atmospheric entry involves a different combination of thermal and mechanical effects from the conditions reproduced in the HiRadMat experiment.

For planetary defense, the study indicates that it may be possible to inject energy deep into a solid or metal rich asteroid without causing it to shatter into many fragments. If energy can be delivered while keeping the body largely intact, deflection methods that rely on imparting a controlled push to the asteroid could become more efficient and predictable. This insight is relevant to concepts that use kinetic impactors as well as to emerging ideas that involve high energy particle beams.

The project was carried out in collaboration with the Outer Solar System Company, which is exploring the feasibility of high energy proton beam systems operating in space. By combining expertise in experimental physics, accelerator technology, and planetary science, the team has opened up a new way to probe the dynamic strength and stability of asteroid materials under conditions that more closely resemble those of real planetary defense scenarios.

The research is reported in the paper Dynamical development of strength and stability of asteroid material under 440 GeV proton beam irradiation, published in the journal Nature Communications. The authors note that further experiments on different meteorite types and structures, as well as complementary numerical modeling, will be needed to build a comprehensive framework for predicting the response of diverse asteroid classes to deflection attempts.

Research Report:Dynamical development of strength and stability of asteroid material under 440 GeV proton beam irradiation

Related Links
University of Oxford
Asteroid and Comet Mission News, Science and Technology