DART Asteroid Impact Created Unexpected Boulder Barrage, Complicating Future Planetary Defense Efforts
New analysis reveals ejected rocks carried three times the momentum of NASA's spacecraft
July 25, 2025
When NASA's Double Asteroid Redirection Test (DART) spacecraft deliberately crashed into the asteroid Dimorphos in September 2022, it achieved its primary goal of demonstrating humanity's first successful planetary defense technology. But new analysis published this month reveals the mission unleashed far more chaos than anticipated—creating a massive barrage of high-speed boulders that carried more than three times the momentum of the spacecraft itself.
The findings, published in the Planetary Science Journal on July 4, 2025, suggest that asteroid deflection for planetary defense is likely far more complex than researchers initially understood.
The Unexpected Discovery
"We succeeded in deflecting an asteroid, moving it from its orbit," said Tony Farnham, lead author of the paper and a research scientist at UMD's Department of Astronomy. "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. That additional factor changes the physics we need to consider when planning these types of missions."
The research team, led by the University of Maryland, analyzed images captured by LICIACube, a small Italian spacecraft that documented the aftermath of the DART impact. Using images taken by LICIACube, the astronomers tracked 104 boulders ranging from 0.2 to 3.6 meters in radius as they shot away from Dimorphos at speeds up to 52 meters per second (116 miles per hour).
"We saw that the boulders weren't scattered randomly in space," Farnham said. "Instead, they were clustered in two pretty distinct groups, with an absence of material elsewhere, which means that something unknown is at work here."
Mission Background and Success
The DART mission launched in November 2021 and traveled for nearly 10 months before impacting Dimorphos on September 26, 2022, successfully altering the asteroid's orbit. This marks humanity's first time purposely changing the motion of a celestial object and the first full-scale demonstration of asteroid deflection technology.
Prior to DART's impact, Dimorphos orbited Didymos once every 11 hours and 55 minutes, and DART's hypervelocity impact shortened this time to 11 hours and 23 minutes – a difference of 32 minutes. The Didymos-Dimorphos system is located approximately 11 million kilometers from Earth and poses no threat to our planet.
Complex Impact Dynamics
The new analysis reveals that the impact was far more violent than the 2005 Deep Impact mission that struck a comet. "Deep Impact hit a surface that was essentially very small, uniform particles, so its ejecta was relatively smooth and continuous," explained Jessica Sunshine, a professor of astronomy and geology at UMD and the paper's second author. "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."
"DART's solar panels likely hit two big boulders, called Atabaque and Bodhran, on the asteroid," Sunshine explained. "Evidence suggests that the southern cluster of ejected material is probably made up of fragments from Atabaque, a 3.3-meter-radius boulder."
Implications for Future Missions
The momentum from the DART impact's ejected boulders was primarily perpendicular to the spacecraft's trajectory, meaning that it could have tilted Dimorphos' orbital plane by up to one degree and potentially sent the asteroid tumbling erratically in space.
"If an asteroid was 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."
ESA's Hera Follow-Up Mission
The European Space Agency's Hera mission, which launched on October 7, 2024, will arrive at the Didymos-Dimorphos system in late 2026 to conduct detailed investigations of DART's impact crater and measure the precise effects of the collision.
On a series of flybys, Hera will survey Dimorphos' mineral makeup and the dust surrounding it. Its mission will also help scientists understand how big the crater is that was created during the DART mission, which they say could help in future asteroid deflections.
Hera also carries two CubeSats called Milani and Juventas which will be deployed to help measure the chemical makeup of Dimorphos' surface and probe its subsurface.
China's Upcoming Planetary Defense Test
China is planning its own asteroid deflection mission, with the China National Space Administration scheduling a 2027 launch that will send one spacecraft to collide with the asteroid 2015 XF261 and another to observe the impact.
The mission will use a single launch to observe and impact a near-Earth asteroid approximately 30 meters in diameter. The observer spacecraft will reach the target asteroid first and conduct three to six months of close observations before the impactor spacecraft performs a high-speed kinetic energy impact test.
The impactor will collide with the asteroid at a speed of 10 kilometers per second in April 2029, when the asteroid is within seven million kilometers of Earth.
The Path Forward
The success of DART is helping to advance theoretical asteroid deflection models and enabling researchers to better understand how – and when – a kinetic impactor spacecraft could be used to deflect an Earth-bound asteroid. However, more research is still needed to fully understand if a kinetic impactor spacecraft would be as effective in mitigating against a more solid object than rubble-pile Dimorphos.
"All of us have a responsibility to protect our home planet. After all, it's the only one we have," said NASA Administrator Bill Nelson. "This mission shows that NASA is trying to be ready for whatever the universe throws at us."
The findings underscore that while humanity has proven it can deflect asteroids, the physics involved are more complex than initially understood—a crucial lesson as we develop our planetary defense capabilities.
Sources
- Farnham, T.L., Sunshine, J.M., et al. (2025). "High-speed Boulders and the Debris Field in DART Ejecta." The Planetary Science Journal. DOI: 10.3847/PSJ/addd1a. Available at: https://arxiv.org/abs/2506.16694v1
- NASA. (2023). "NASA Confirms DART Mission Impact Changed Asteroid's Motion in Space." NASA News Release. Available at: https://www.nasa.gov/news-release/nasa-confirms-dart-mission-impact-changed-asteroids-motion-in-space/
- University of Maryland. (2025). "Massive Boulders Ejected During DART Mission Complicate Future Asteroid Deflection Efforts." College of Computer, Mathematical, and Natural Sciences. Available at: https://cmns.umd.edu/news-events/news/massive-boulders-ejected-during-dart-mission-complicate-future-asteroid-deflection
- NASA Science. (2025). "Planetary Defense - DART." Available at: https://science.nasa.gov/planetary-defense-dart/
- European Space Agency. (2024). "Hera." Available at: https://www.esa.int/Space_Safety/Hera
- The Planetary Society. (2024). "China targets its first planetary defense test mission." Available at: https://www.planetary.org/articles/china-targets-its-first-planetary-defense-test-mission
- SpaceNews. (2024). "China reschedules planetary defense mission for 2027 launch." Available at: https://spacenews.com/china-reschedules-planetary-defense-mission-for-2027-launch/
- NPR. (2024). "A European spacecraft launches to perform a crash scene investigation on an asteroid." Available at: https://www.npr.org/2024/10/07/nx-s1-5144223/hera-spacex-asteroid-mission-dimorphos
- Wikipedia. (2025). "Double Asteroid Redirection Test." Available at: https://en.wikipedia.org/wiki/Double_Asteroid_Redirection_Test
- Wikipedia. (2025). "Hera (space mission)." Available at: https://en.wikipedia.org/wiki/Hera_(space_mission)
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