BALTIMORE—Second by second, as a NASA satellite hurtled toward a pile of rocks in space, scientists gathered at the Johns Hopkins University Applied Physics Laboratory issued their unfiltered analysis.
“It doesn’t look like any asteroid I’ve ever seen!”
“That’s totally a rubble pile—I knew it!”
In the final moments of the Double Asteroid Redirection Test (DART), researchers who had spent years designing and simulating the spacecraft’s collision with the moon of a larger asteroid were glued to the TV. They greeted each new image with heartier applause. Then, the screen flashed bright red as the satellite lost signal on impact.
The scientists’ tear-stained cheeks lit up with reflected light, and the crowd erupted. A bouquet of fireworks sprouted from behind the building. Humanity’s first-ever planetary defense test—which could one day help scientists deflect an asteroid on a collision course with our planet—was, quite literally, a smashing success.
Some in the room were simply dumbfounded. “I’m stumped,” says Jessica Sunshine, a planetary scientist at the University of Maryland (UMD), College Park, and DART investigator. “We knew it was going to be exciting, and I thought it was going to work, but nobody could have predicted that.”
Though measurements from the impact will keep scientists busy for months to come, one early surprise came from DART’s images of the double-asteroid system just before the crash. From previous radar observations, astronomers had a hazy idea that the larger body would be shaped like a spinning top. “But [its] shape was way different … it was so flattened compared to what we expected,” says Harrison Agrusa, an astronomer at UMD and DART member.
Meanwhile, the smaller asteroid—DART’s ultimate target—appeared shockingly spherical. The moon’s symmetrical rubble-pile structure hints that it may have formed from material shed off the parent body as it spun, Agrusa adds. Knowing the shape and composition of these celestial objects will help astronomers better understand their origins and orbits.
The DART satellite, roughly the size and mass of a cow, was launched in November 2021 toward a 780-meter asteroid named Didymos. Ten months later, about an hour before impact, the spacecraft spied its final resting place: Dimorphos, the 160-meter-wide moon. The DART team members had prepared a series of last-second emergency maneuvers in case the satellite’s autonomous navigation malfunctioned, but in the end, they didn’t have to touch a thing. As planned, DART crashed into its target at 6 kilometers per second.
“We are so excited to be done,” says Elena Adams, a DART mission systems engineer. “I can finally sleep.”
But not everyone was off to bed so quickly. Halfway across the globe and late into their night, two astronomers huddled in a lounge of the South African Astronomical Observatory. When DART’s transmission cut to red, Amanda Sickafoose and Nicolas Erasmus turned their heads to footage of the impact they’d captured with the Lesedi telescope. They hoped to see confirmation in the form of a gradual brightening of the asteroid system, as dust and rocks knocked off the asteroid would reflect more sunlight toward the telescope. What they got was even clearer: Within seconds of the impact, they watched in exquisite detail as the asteroid sneezed out a plume of ejecta. “We were astonished,” Sickafoose says.
Dozens of astronomers—professional and amateur—from all seven continents watched the collision in real-time. Through the night, scenes captured by observatories circled through DART’s internal channels.
“The entire team was going bonkers,” says Alan Fitzsimmons, an astronomer at Queen’s University Belfast and DART observer. “The data is just incredible. … You couldn’t have asked for a better test of a kinetic impactor.”
Over the next few days, LICIACube, a small satellite that DART ejected 2 weeks before the crash, will release more images of the asteroids. Meanwhile, the James Webb and Hubble space telescopes will get better pictures of the cloud of ejecta streaming from the surface. By studying the change in light from the system, scientists will seek to decode the change in the moon’s orbit, which will indicate how effective DART’s strike was in altering its trajectory.
For now, NASA scientists are hailing the test mission as a success. Still, a major challenge remains in humanity’s ability to thwart threatening space rocks: “We can’t use these techniques unless we know where the objects are,” says Amy Mainzer, an astronomer at the University of Arizona. “If you can’t find them, you certainly can’t deflect them.”
Of the Dimorphos-size asteroids that could destroy a large city or small country, astronomers estimate they’ve only found about 40%. NASA has plans to identify and track 90% of these looming threats with NEO Surveyor, a space-based telescope led by Mainzer. But because of a lack of funding, the mission remains delayed until at least 2026.
Some hope DART’s success will help fuel the effort to identify lingering planetary threats. Yesterday, we couldn’t be sure we could divert an asteroid barreling toward Earth. “Today, we can,” Fitzsimmons says. “DART has basically shown us that we are not like the dinosaurs. So, let’s find those asteroids … and let’s do something about it.”
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