In September 2022, NASA did something audacious: it deliberately crashed a spacecraft into an asteroid at roughly 22,500 kilometres per hour, just to see what would happen. Three and a half years later, the full picture has finally come into focus — and it's even more remarkable than anyone dared hope.
A comprehensive new study published in Science Advances has confirmed that the Double Asteroid Redirection Test (DART) didn't merely shove the small moonlet Dimorphos into a tighter orbit around its parent asteroid, Didymos. It shifted the entire two-asteroid system's path around the Sun — the first time humanity has measurably altered the orbit of a natural object in our solar system.
"This study marks a notable step forward in our ability to prevent future asteroid impacts on Earth," wrote the international research team, led by aerospace engineer Rahil Makadia of the University of Illinois at Urbana-Champaign.
What DART actually did
The mission's target was a binary asteroid system: Didymos, roughly 800 metres across, and its smaller companion Dimorphos, about the size of a football stadium at 170 metres wide. Neither poses any threat to Earth — they were chosen because Dimorphos's orbit was extremely well characterised, making any changes easy to spot.
When the 610-kilogram DART probe slammed into Dimorphos, it shortened the moonlet's orbital period around Didymos by a staggering 33 minutes. Scientists had hoped for seven. That alone was cause for celebration, but the bigger question lingered: could such an impact meaningfully shift an asteroid's course through the solar system?
The answer is yes — and here's how they proved it
To find out, Makadia's team embarked on a painstaking detective operation. They gathered data from 22 stellar occultations — moments when the asteroid passed in front of a distant star, causing a brief blink visible from Earth — along with nearly 6,000 ground-based measurements collected over 29 years.
The result? DART changed the entire Didymos system's orbital velocity by about 11.7 micrometres per second — roughly 42 millimetres per hour, or about the width of a watch face. That might sound negligible, but in the vast timescales of space, small nudges compound dramatically.
"This is a tiny change to the orbit, but given enough time, even a tiny change can grow to a significant deflection," said Thomas Statler, NASA's lead scientist for solar system small bodies. Over a decade, that minuscule push would accumulate to a 3.69-kilometre shift in position — more than enough to steer a hazardous asteroid safely past Earth, given sufficient warning.
The surprise bonus: an asteroid "rocket plume"
One of the study's most intriguing findings was about what happened after impact. When DART struck Dimorphos, it blasted a plume of pulverised rock and dust into space. That debris carried its own momentum — effectively doubling the push.
"The material kicked up off an asteroid surface acts like an extra rocket plume," Makadia explained. Scientists measured the momentum enhancement factor — known as beta — at roughly two, meaning the debris gave the asteroids an additional shove equal to the spacecraft's initial impact.
The study also revealed that Dimorphos is surprisingly lightweight — a fluffy, loosely bound "rubble pile" of boulders and dust with a density of just 1.51 tonnes per cubic metre. "This was a real surprise," Makadia said. "We previously didn't know anything about the density of Dimorphos."
What comes next
The findings arrive at a pivotal moment for planetary defence. The European Space Agency's Hera spacecraft is on course to reach the Didymos system later this year, where it will study the DART impact crater up close and take precise measurements of both asteroids' mass and structure.
"It's a high-fidelity instrument that hopefully will give us confirmation of what we believe," Makadia said. "Plus, there are always new things to be found out when we visit an asteroid. I'm very excited about when Hera gets there."
For now, the message is as reassuring as it is awe-inspiring: when the day comes that a threatening asteroid is spotted heading our way, we've already proven we can do something about it. Humanity's first cosmic punch landed — and it landed hard.
