In 2022, NASA slammed a spacecraft into an asteroid moonlet at 14,000 mph; humanity’s first planetary-defense test shortened its orbit by about 32 minutes

The National Aeronautics and Space Administration has done what has never been attempted by any other civilization before: in September 2022, it targeted an asteroid 6.8 million miles away from Earth and deliberately slammed it head-on using a vending machine-sized spacecraft flying at around 14,000 miles per hour.

This mission had nothing to do with astronauts, nor did it have anything to do with any Bruce Willis-like heroic monologues; it only featured a robotic probe named DART (Double Asteroid Redirection Test), which was livestreaming its own destruction as it hit Dimorphos, an asteroid.

According to NASA’s own reports, the last images captured by the craft were cut off the moment it made contact. This is one of the most anticlimactic, yet most reassuring, ways for any space exploration mission to end. For people whose lives have been shaped by asteroid apocalypse films, this was the real thing without the drilling rigs and Aerosmith songs playing in the background.


So did it actually move the thing?

The portion of this story that deserves more recognition than it has received is this: Dimorphos is not a solitary object flying through space. Rather, it is a "moonlet" revolving around a bigger asteroid known as Didymos, and that made it an ideal test subject; the orbital period of the moonlet could be measured before and after impact from telescopes on Earth, no follow-up mission required.

Dimorphos orbited Didymos in an 11-hour and 55-minute cycle prior to DART. As noted in NASA's press release confirming the results of the mission, the impact resulted in a decrease of Dimorphos' orbital period by at least 32 minutes, far surpassing the mission’s minimum threshold of a 73-second change. A peer-reviewed 2023 study titled “Orbital period change of Dimorphos due to the DART kinetic impact,” published in Nature magazine and led by Cristina Thomas from Northern Arizona University, among others, later refined that figure to 33.0 ± 1.0 minutes.

The plot twist nobody expected

That's when it got really exciting and perhaps humbling for the engineers responsible for this mission. DART weighed around 1,260 pounds. Ideally, had it been a perfectly clean strike, the effect of such an impact on Dimorphos should have been no greater than seven minutes, based on billiard-like collision physics: the momentum of the spacecraft alone, transferred directly to a body many thousands of times its mass. Instead, the measured movement was roughly four to five times greater than that clean-hit estimate.

The reason for it is quite simple, as the impact sent huge amounts of rock and debris as ejecta into space, which acted as another force, propelling the asteroid in a new direction. According to Cheng et al., in another 2023 study titled “Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos,” published in Nature, the "momentum enhancement factor" in this collision amounted to approximately 3.6, which means the ejecta played a much bigger role in deflecting Dimorphos than the actual impact.

Why this matters

This may seem like just another "cool NASA thing," but that's only because Dimorphos posed absolutely no danger to us. And that's why this was chosen in the first place. The DART experiment showed that should a similar-sized object as Dimorphos, about 525 feet across, ever be discovered on a collision course with Earth, an appropriately sized and affordable spacecraft deployed years in advance, could make a very real difference.

That isn't hypothetical anymore. This is a proven, peer-reviewed, repeatable demonstration of a real solution, and as a species fixated on existential risk, we should pay more attention.