DART's Lasting Scientific Legacy
When NASA's DART spacecraft slammed into the asteroid Dimorphos in September 2022, the primary goal was to test whether a kinetic impactor could alter an asteroid's orbit. That mission succeeded spectacularly. But scientists poring over the detailed images captured during DART's final approach have now discovered something unexpected: direct evidence that the binary asteroid system had been exchanging surface material long before the spacecraft arrived.
A new study published in The Planetary Science Journal by Jessica Sunshine and colleagues at the University of Maryland describes fan-shaped patterns of material spread across the surface of Dimorphos. These patterns, initially suspected to be imaging artifacts, have been confirmed as real geological features — and they tell a story of material flowing between Dimorphos and its larger companion, Didymos.
Deciphering the Fan Patterns
The fan-like features appear as streaks of material radiating across Dimorphos's rubble-pile surface. Their orientation and distribution are consistent with debris ejected from Didymos landing on the smaller moon, carried there by the weak but persistent gravitational interactions between the two bodies.
Binary asteroid systems — where two asteroids orbit each other — are surprisingly common, comprising an estimated 15 percent of near-Earth asteroids. Theoretical models have long predicted that these systems should exchange surface material through various mechanisms, including tidal forces, impacts on one body that loft debris onto the other, and the gradual migration of loose regolith driven by the YORP effect, a process where uneven absorption and re-emission of sunlight creates tiny but cumulative torques.
Despite these predictions, direct observational evidence of material transfer had remained elusive until now. The DART mission's close-approach images provided the resolution needed to identify these features for the first time.
