NASA's asteroid target practice may not have been the success we thought

When NASA smacked an asteroid with a spacecraft the size of a vending machine in 2022, the mission was rather quickly declared a victory. 

DART, short for Double Asteroid Redirection Test, sought to prove whether humans could one day nudge a killer space rock off course. The crash did, in fact, shift the harmless moonlet Dimorphos' orbit by 33 minutes. But new research led by the University of Maryland suggests the results of that target practice are way less clear-cut than anyone imagined.

Dimorphos didn't just wobble — it recoiled, spun slightly off its axis, and shifted its tilt after the choreographed crash, according to the study, flinging boulders in surprising directions. Some of those rocks were as big as pickup trucks, moving at speeds up to 116 mph, with more than three times the momentum of the spacecraft that hit it.

The chaotic outcome could be a problem if earthlings ever need to use this method for real to save the planet. Tony Farnham, lead author of the paper published in The Planetary Science Journal, said scientists will need to consider these complicated physics when planning potential asteroid deflection missions in the future.

"We succeeded in… moving it from its orbit," Farnham said in a statement. But "while the direct impact of the DART spacecraft caused this change, the boulders ejected gave an additional kick that was almost as big."

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NASA broadcast the $330 million space collision on Sept. 26, 2022. Through a camera on the uncrewed spacecraft, the public was able to watch a 525-foot rock grow from a mere dot of light to a bumpy egg-shaped mass that blotted out the whole frame. The live feed almost kept up with the crash in real time, with only a 45-second delay, providing a front-row seat to an event happening 6.8 million miles away.

Millions of space rocks orbit the sun. The majority are in the main asteroid belt between Mars and Jupiter, but occasionally rocks get shoved into the inner solar system, relatively closer to Earth.

There are currently no known asteroids on an impact course with the planet. Still, scientists are keeping a watchful eye on nearly 40,000 large objects out there with the hope of avoiding the fate of the dinosaurs. Astronomers believe there could be thousands more awaiting discovery.

Even smaller rocks can cause immense destruction. An undetected meteor exploded over Chelyabinsk, Russia, in February 2013, causing an airburst and shockwave that affected six cities and injured 1,600 people. The rock was just 60 feet across, according to NASA.

The DART spacecraft takes its final full picture of Dimorphos, an asteroid moonlet of Didymos, as it approaches at 14,000 mph. Credit: NASA / Johns Hopkins APL

Using images taken by LICIACube, a toaster-size spacecraft supplied by the Italian Space Agency, Farnham's team created a 3D map of the collision's aftermath and tracked 104 boulders that blasted away from Dimorphos. This little spacecraft showed up on the scene just three minutes after the hit. 

The data reveal that a massive amount of the force that moved the asteroid didn't come from the DART spacecraft but how the rocks and dust scattered. A cluster of large boulders ejected almost perpendicular to the direction of the impact. Essentially, that means the asteroid's surface blew sideways — something no one anticipated. 

Curiously, rocks gathered into two distinct groups, with little debris elsewhere. The larger of the two swarms was tossed south at high speed. The team thinks perhaps those boulders came from contact with DART's solar panels right before the main body hit the surface. 

"Something unknown is at work here," Farnham said. 

NASA's Hubble Space Telescope spotted dozens of boulders drifting from asteroid Dimorphos — space shrapnel flung loose after the agency's DART mission intentionally crashed a spacecraft into it. Credit: NASA / ESA / David Jewitt / Alyssa Pagan

Until now, most of the focus has been on the dust cone that exploded in the direction opposite to DART's approach, but that number only tells part of the story. The new findings suggest the sideways momentum from the boulder plume could be several times that number.

Knowing exactly how an impact unfolds — where energy goes, how debris moves, and what parts of an asteroid respond — will inform how NASA aims in the future. Hit too hard or in the wrong spot, and you might not nudge a rock but spin it, split it, or make things worse.

NASA and the European Space Agency's Hera mission, scheduled to arrive at the scene next year, will see what Dimorphos is up to now. If it's tumbling or orbiting its parent asteroid in an off-kilter way, that'll be a clear sign these boulders made a bigger mess than scientists realized — and provide a valuable lesson. All of these subtleties are crucial to understand in the event of an emergency, said Jessica Sunshine, a coauthor. 

"You can think of it as a cosmic pool game," she said in a statement. "We might miss the pocket if we don't consider all the variables."