A pioneering study led by the University of Maryland has uncovered that asteroid systems are significantly more dynamic than previously understood. Rather than merely orbiting each other, these celestial bodies can exchange rocks and dust through gentle impacts, slowly reshaping their surfaces over extensive periods.
This revelation stems from detailed analysis of images taken by NASA's Double Asteroid Redirection Test (DART) spacecraft in 2022, prior to its deliberate collision with the asteroid moon Dimorphos. The research team observed bright, fan-shaped streaks on Dimorphos, providing the first direct visual evidence of material transfer between asteroids. These findings were published on March 6, 2026, in The Planetary Science Journal, enhancing our understanding of asteroids that could pose a future threat to Earth.
Lead author Jessica Sunshine, a professor at UMD, initially suspected camera malfunctions or image processing errors when the streaks appeared. However, upon further investigation, the patterns aligned with low-velocity impacts, akin to "throwing cosmic snowballs," marking the first concrete proof of recent material movement in a binary asteroid system.
YORP Effect Confirmation
The study also confirms the Yarkovsky-O'Keefe-Radzievskii-Paddak (YORP) effect, where sunlight gradually increases the rotation of small asteroids. As their spin accelerates, loose surface material can be ejected, potentially forming small moons. Sunshine noted that this phenomenon likely occurred in the Didymos system, where debris from Didymos landed on Dimorphos.
Uncovering Streaks in DART Imagery
Identifying these streaks required months of meticulous analysis. The patterns were initially obscured in the raw images from DART. UMD researchers developed innovative techniques to eliminate shadows and lighting artifacts, revealing the subtle streaks left by the "cosmic snowballs."
Research scientist Tony Farnham expressed astonishment at the unique patterns observed, which had never been documented before. The consistent lighting during DART's approach posed challenges in discerning genuine features from optical illusions. However, the team confirmed the authenticity of the streaks by tracing them to a specific area on Dimorphos.
Asteroid Debris Dynamics
Previous indirect evidence suggested that sunlight could enhance the spin of small asteroids, leading to surface material ejection. The new models from the UMD team provide visual confirmation of this process and indicate where debris from Didymos landed on Dimorphos, traveling at a leisurely 30.7 centimeters per second--slower than a typical walking pace.
Laboratory Simulations of Cosmic Interactions
To validate their findings, researchers conducted experiments at UMD's Institute for Physical Science and Technology, simulating asteroid conditions. High-speed cameras documented how marbles dropped into sand with gravel produced patterns similar to those on Dimorphos, confirming the influence of surface boulders on incoming material.
Future Insights from the Hera Mission
The European Space Agency's Hera mission, set to reach Didymos in December 2026, aims to investigate whether the streak patterns survived the DART impact. Sunshine and her team anticipate that Hera could uncover new patterns formed by debris dislodged during the collision.
Sunshine emphasized the importance of these findings for understanding near-Earth asteroids and their evolution. The research indicates that these systems are far more dynamic than previously believed, enhancing models and planetary defense strategies.