There’s something subtly unnerving about the term “cosmic snowballs.” It sounds almost lighthearted, the kind of language used by science instructors to keep students engaged. However, Jessica Sunshine of the University of Maryland initially felt doubt rather than wonder when she noticed faint fan-shaped streaks across Dimorphos’ surface in photos taken just before NASA’s DART spacecraft crashed into it. “At first, we thought something was wrong with the camera,” she replied. That response seems sincere. Seldom does true discovery come with much fanfare.
For a spacecraft that vanished on impact, the DART mission has been producing new discoveries at a rate that seems almost unheard of. The first-ever intentional test of asteroid deflection took place in September 2022 when the probe struck Dimorphos, a small asteroid moon circling its larger companion Didymos. Dimorphos’s orbital period around Didymos was shortened by about thirty-two minutes as a direct consequence. Quietly, scientists were happy. Things became more intriguing when the longer-term data began to come in.
| NASA DART Mission — Key Facts & Profile | Details |
|---|---|
| Mission Full Name | Double Asteroid Redirection Test (DART) |
| Mission Type | First planetary defense technology demonstration |
| Target Asteroid | Dimorphos — moon of the larger asteroid Didymos |
| Dimorphos Diameter | Approximately 160 metres |
| Didymos Diameter | Approximately 780 metres |
| Impact Date | September 26, 2022 |
| Distance from Earth at Impact | Roughly 11 million kilometres |
| Travel Duration | 10 months to reach target system |
| Orbital Change Achieved | Dimorphos orbit around Didymos shortened by ~32 minutes |
| Heliocentric Orbit Change | System’s solar orbit slowed by 11.7 microns per second (~360 metres per year) |
| Key Research Institution | University of Maryland, University of Illinois Urbana-Champaign |
| Further Reading | New findings published in Science Advances, March 2026 |
Research that was published in Science Advances in March 2026 verified what no one had previously noticed: the collision changed the binary system’s entire orbit around the sun, not just Dimorphos. In terms of speed reduction, the change was almost ridiculously tiny: 11.7 microns per second, or roughly 360 meters per year, or one-tenth the width of a human hair. That number might seem insignificant to the majority of people. It isn’t. The study’s principal investigator, Rahil Makadia, a planetary defense researcher at the University of Illinois Urbana-Champaign, stated simply: “Over time, such a small change in an asteroid’s motion can make the difference between a hazardous object hitting or missing our planet.”
An entirely new layer is added by what the streaks on Dimorphos’s surface revealed. These fan-shaped marks, according to scientists, were created over millions of years by slow debris transfers between Dimorphos and Didymos, where material spun off the larger body, drifted across the gap, and landed in gentle, low-velocity impacts. A series of photos taken eight seconds prior to a planned collision show a process reshaping asteroid surfaces over geological timescales. The idea that these two rocks have been silently exchanging material for a very long time before humans existed and that we only became aware of it when we crashed something into one of them is worth considering.
Since binary systems are thought to make up 15% of near-Earth asteroids, comprehending these dynamics is more than just academic. Both Dimorphos and Didymos have visible ridges along their equators due to the YORP effect, which causes sunlight to gradually spin an asteroid faster until material sheds from its surface. NASA’s Lucy spacecraft observed similar features on the asteroid Dinkinesh. These shapes are not arbitrary. They are documents of an ongoing process.
Whether the full implications of this mission have become widely recognized as they most likely should is still up for debate. There’s a sense that scientists are just starting to comprehend what they truly accomplished in those ten months of flight and one moment of impact as they watch the data accumulate over three years—radar measurements accurate to within ten to fifteen meters across millions of kilometers combined with stellar occultation tracking. The original reasoning was straightforward, according to Derek Richardson, an emeritus professor of astronomy at the University of Maryland: striking a binary system allowed the team to measure orbital changes much more quickly than tracking a single asteroid circling the sun. A neat solution to a hard measurement problem.
The 1908 Tunguska event and the 2013 Chelyabinsk meteor, which exploded in the atmosphere and injured people on the ground, are two significant events that have affected Russia in the last century. As of right now, no known asteroid poses a threat to Earth. However, there is now proven and documented technology to step in if someone ever needs to. That’s a big deal.
