NASA’s DART images reveal dust and debris moving between the binary asteroids Didymos and Dimorphos.
Credit : iopscience.iop.org
New images captured by NASA’s DART spacecraft have revealed something scientists had never clearly observed before: two asteroids slowly exchanging dust and debris while orbiting each other in space. The discovery shows that some near-Earth asteroids are far more dynamic than previously thought, with material gently drifting from one body to another over time.
The phenomenon was spotted in images taken shortly before the famous 2022 DART collision with the asteroid moon Dimorphos. After analysing the photographs in detail, researchers discovered faint streaks across the surface of the asteroid moon – evidence that particles from the larger asteroid Didymos had travelled across space and landed on its companion.
For scientists studying asteroid behaviour, the finding is significant. Understanding how these rocky bodies evolve helps researchers improve planetary defence models, which are used to predict how asteroids might behave if they ever posed a threat to Earth.
NASA’s DART mission reveals hidden activity in binary asteroids
When NASA launched the Double Asteroid Redirection Test (DART) mission, the goal was straightforward: deliberately crash a spacecraft into Dimorphos to test whether humanity could deflect a potentially dangerous asteroid.
But the mission’s final images before impact turned out to contain an unexpected clue.
Scientists later noticed fan-shaped streaks spreading across the asteroid’s surface. At first, the marks were so faint that researchers wondered whether they were simply camera artefacts or errors in image processing.
After months of analysis and digital enhancement, the patterns revealed something far more interesting.
Researchers from the University of Maryland concluded that the streaks were caused by slow-moving particles drifting from Didymos to Dimorphos. These particles – essentially tiny fragments of rock and dust – travelled at extremely low speeds before landing on the asteroid moon.
Instead of creating impact craters, the debris settled gently on the surface, leaving distinctive ray-like patterns.
Jessica Sunshine, the study’s lead author, described the process as being similar to “cosmic snowballs” landing softly on the asteroid’s surface.
A space phenomenon scientists had only predicted before
Until now, scientists suspected that such exchanges of material could occur in binary asteroid systems, but there had been no direct visual evidence.
Binary asteroids are pairs of space rocks where one body orbits another. According to researchers, around 15 percent of near-Earth asteroids belong to such systems, often with a larger primary asteroid and a smaller moon.
In this case, the larger asteroid Didymos likely shed material because of a well-known physical effect called the YORP effect.
This process occurs when sunlight gradually changes the spin of a small asteroid. Over long periods, the rotation can accelerate enough that loose surface material lifts off and drifts away.
Some of that debris may eventually gather into a small moon – which scientists believe is how Dimorphos itself originally formed.
The new images suggest that this material does not simply disappear into space. Instead, some of it can slowly drift back and settle on the smaller asteroid.
How scientists uncovered the hidden streaks
The evidence wasn’t immediately visible in the raw spacecraft images.
Researchers had to develop specialised image-processing techniques to remove shadows cast by large boulders on the asteroid’s surface. Once those lighting effects were filtered out, the fan-shaped streaks began to appear clearly.
At first, scientists struggled to confirm whether the patterns were real or simply illusions created by sunlight.
However, detailed 3D modelling of the asteroid’s surface helped verify that the streaks originated from a specific area near the moon’s edge — strongly suggesting that external particles had struck the surface at low speed.
Further calculations showed that the debris was travelling at only around 30 centimetres per second, slower than the pace of a normal human walking.
That slow speed explains why the particles formed deposits instead of leaving impact craters.
Even tiny dust movements can reshape asteroids
Although the dust exchanges might seem minor, scientists say the process could have important long-term effects.
Asteroids have extremely weak gravity. That means even gentle impacts or slow movements of debris can gradually reshape their surfaces over millions of years.
Dust deposits, shifting rocks and subtle changes in rotation can all influence how an asteroid evolves – and potentially how it might react to future impacts.
Understanding these processes is crucial for planetary defence research, which aims to predict how asteroids behave and how they might be deflected if necessary.
Lab experiments helped confirm the theory
To test whether the patterns seen on Dimorphos made sense, scientists carried out laboratory experiments on Earth.
Researchers dropped marbles into trays of sand mixed with small painted stones designed to mimic the asteroid’s rocky surface.
High-speed cameras revealed something striking: larger rocks on the surface redirected the incoming material, creating fan-shaped streaks of debris almost identical to those seen on Dimorphos.
Computer simulations carried out at Lawrence Livermore National Laboratory produced similar results, reinforcing the idea that the streaks were caused by particles drifting from Didymos.
A new mission could confirm the discovery
Scientists may soon get a closer look at the Didymos–Dimorphos system.
The European Space Agency’s Hera mission is scheduled to arrive at the asteroid pair in December 2026. Hera will study the aftermath of the DART collision and examine both asteroids in unprecedented detail.
Researchers hope the spacecraft will confirm whether the dust streaks survived the impact and perhaps even reveal new patterns created by debris released during the collision.
If confirmed, the discovery would strengthen the idea that binary asteroids are far more active and complex than scientists once believed.
And for planetary defence experts, that knowledge could prove crucial when planning future missions designed to protect Earth from potential asteroid threats.
