Planetary defense experts are now saying NASA’s DART asteroid redirection mission may have inadvertently made future asteroid deflections much more challenging after its test sent boulders hurtling through space on unexpected trajectories.
In September 2022, the DART mission successfully altered the orbit of asteroid moon Dimorphos. Unfortunately, the smaller space rocks that were dislodged when the kinetic impactor struck the natural satellite achieved three times the momentum of the spacecraft that created them.
The University of Maryland-led team (UMD) behind the new research paper on DART’s repercussions cautions that results demonstrate planetary defense may be considerably more complex than previously suspected, with the potential for many unintended consequences.
Moving an Asteroid from Its Orbit
“We succeeded in deflecting an asteroid, moving it from its orbit,” said lead author Tony Farnham, 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,” Farnham said.
The researchers’ data came from an Italian cubesat named LICIACube, which was sent to follow up on the DART mission, as Earth-based observations would be inadequate for deriving precise measurements from the aftermath. In the LICIACube images, the team identified 104 boulders moving at speeds of up to 116 miles per hour and tracked their trajectories in three dimensions. These newly independent space rocks range in diameter from 0.2 to 3.6 meters.
Analyzing the Impact
“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.”
Based on the craft’s impact, the team believes that its solar panels broke up larger boulders on Dimorphos’ surface before the main body hit. That first part of the impact most likely created the largest debris cluster, which holds roughly 70% of the known objects. This cluster raced away from the asteroid at high velocity.
“DART’s solar panels likely hit two big boulders, called Atabaque and Bodhran, on the asteroid,” said second author Jessica Sunshine, a professor of astronomy and geology at UMD. “Evidence suggests that the southern cluster of ejected material is probably made up of fragments from Atabaque, a 3.3-meter-radius boulder.”
Outlook on Planetary Defense
Sunshine was also deputy principal investigator on a somewhat similar mission, Deep Impact, in which a NASA probe impacted the Tempel 1 comet to study its interior. Yet, very different conditions between the two space objects yielded highly divergent results.
“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.”
“Comparing these two missions side-by-side gives us this insight into how different types of celestial bodies respond to impacts, which is crucial to ensuring that a planetary defense mission is successful,” Sunshine said.
The new work provides essential knowledge for the European Space Agency’s upcoming Hera missions, which will enter the Didymos-Dimorphos system in 2026.
“Data gathered from LICIACube provides additional perspectives on impact events, especially as DART was originally designed to solely rely on Earth-based observations,” Farnham said. “Hera will do the same by giving us another direct view of the impact’s aftermath, relying on the predictions we’ve made using data gathered from DART.”
Acquiring all possible data about this early planetary defense mission will be essential for astronomers to fully understand the physics and consequences of deflecting space objects.
“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,” she added. “We might miss the pocket if we don’t consider all the variables.”
The paper “Massive Boulders Ejected During DART Mission Complicate Future Asteroid Deflection Efforts” appeared on July 4, 2025, in The Planetary Science Journal.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.