Massive Boulders Ejected by DART Mission Could Complicate Future Asteroid Deflection

When NASA's DART spacecraft smashed into the asteroid moon Dimorphos in 2022, it was more than proof that a kinetic impactor can nudge the orbit of an asteroid. The impact created about 100 large boulders, some of which had greater than three times the spacecraft's momentum. These high-speed ejecta added unanticipated forces that may complicate future planetary defence efforts. Using data from Italy's LICIACube—an observer satellite deployed during the mission—a University of Maryland-led team tracked the rocks' locations and velocities, revealing a complex and potentially disruptive impact legacy.

DART's Boulder Ejecta Could Disrupt Asteroid Deflection, New Study Warns of Hidden Forces

As per a study in Planetary Science Journal published on July 4, 2025, the team discovered that the boulders weren't scattered randomly but instead clustered into two clear groups, indicating unknown mechanisms at work. Lead author Tony Farnham noted that this added momentum, largely perpendicular to the spacecraft's trajectory, might have tilted Dimorphos' orbit and introduced unpredictable rotation. The largest cluster, travelling southward at shallow angles, likely originated from two larger surface boulders struck moments before the main impact.

Second author Jessica Sunshine explained that DART's solar panels may have shattered these large boulders, Atabaque and Bodhran, creating chaotic debris patterns. In contrast to NASA's earlier Deep Impact mission—which hit a dustier target and produced smoother ejecta—DART's rocky terrain resulted in filamentary structures. The results emphasise how varied the surfaces of asteroids can be and how that variety can affect the practicality of deflection techniques, complicating mission-level planning.

The debris kicked out would transfer momentum, shifting the asteroid's orientation in space — an aspect that had not been accounted for in previous models. Unaccounted for, these forces may have led to future missions missing their deflection targets. Sunshine emphasised that such subtle forces are critical, likening future planetary defence efforts to “a cosmic pool game” where missing a shot could have planetary consequences.

ESA's Hera mission, to the Didymos-Dimorphos system in 2026, will demonstrate these predictions and reveal more about the physics of the boulder-flying impact. The need for two points of view is already apparent from the LICIACube data, Farnham stressed. With Hera's help, researchers aim to refine their models to better prepare for the next real-life asteroid threat.