When NASA‘s Double Asteroid Redirection Test (DART) spacecraft intentionally crashed into the asteroid Dimorphos on Sept. 26, 2022, it successfully altered the asteroid’s path. However, a new study reveals that the impact also blasted a swarm of boulders into space, creating a powerful secondary “kick” that could complicate future efforts to deflect potentially hazardous asteroids. The research, led by astronomers at the University of Maryland and published in The Planetary Science Journal, shows that the momentum—a measure of an object’s mass in motion—from this ejected debris was surprisingly powerful, adding a new variable to the physics of asteroid deflection.

Using images from LICIACube, an Italian satellite that witnessed the aftermath of the collision, the team tracked 104 boulders, ranging in radius from less than a meter to 3.6 meters. These rocks were launched from Dimorphos at speeds reaching 52 meters per second, or more than 116 mph. “Our research shows that while the direct impact of the DART spacecraft caused this change, the boulders ejected gave an additional kick that was almost as big,” said Tony Farnham, the study’s lead author and a research scientist at the University of Maryland’s Department of Astronomy, in a university press release. “That additional factor changes the physics we need to consider when planning these types of missions.”

The boulders were not ejected uniformly. Instead, they formed distinct clusters, with the largest group moving south, nearly at right angles to the spacecraft’s path. This suggests a more complex event than a simple cratering impact. Researchers believe DART’s solar panels may have first struck and shattered larger surface boulders, creating the debris. Jessica Sunshine, a professor at the University of Maryland and the paper’s second author, contrasted this with a previous mission. “Deep Impact hit a surface that was essentially very small, uniform particles, so its ejecta was relatively smooth and continuous,” Sunshine explained. “And here, we see that DART hit a surface that was rocky and full of large boulders, resulting in chaotic and filamentary structures in its ejecta patterns.”

The powerful, sideways blast of boulders had enough momentum to potentially tilt Dimorphos’s orbital plane by up to one degree and send it tumbling. These effects will be a key focus for the European Space Agency‘s Hera mission, which is set to arrive at the asteroid system in 2026 to study the long-term aftermath. The findings underscore the importance of understanding an asteroid’s surface composition before attempting to move it. “If an asteroid [were] tumbling toward us, and we knew we had to move it a specific amount to prevent it from hitting Earth, then all these subtleties become very, very important,” Sunshine added. “You can think of it as a cosmic pool game. We might miss the pocket if we don’t consider all the variables.”

References

• Farnham, T. L., Sunshine, J. M., Hirabayashi, M., Ernst, C. M., Daly, R. T., Agrusa, H. F., Barnouin, O. S., Li, J.-Y., Kumamoto, K. M., Syal, M. B., Wiggins, S. E., Bjonnes, E., Stickle, A. M., Raducan, S. D., Cheng, A. F., Glenar, D. A., Lolachi, R., Stubbs, T. J., Fahnstock, E. G., … Zinzi, A. (2025). High-speed boulders and the debris field in dart ejecta. The Planetary Science Journal, 6(7), 155. https://doi.org/10.3847/PSJ/addd1a
• Jiang, G. & University of Maryland. (2025, July 8). Massive boulders ejected during DART mission may complicate future asteroid deflection efforts. Phys.Org; University of Maryland. https://phys.org/news/2025-07-massive-boulders-ejected-dart-mission.html