What DART has taught us so far

Scoring a bulls-eye

Just two weeks after impact, NASA confirmed that DART changed the orbit of Dimorphos around Didymos. Whereas it once took Didymos 11 hours and 55 minutes to make an orbit, it now takes 11 hours and 32 minutes. This far exceeded the mission’s minimum success criteria of shortening the orbital period by 73 seconds.

The conclusion was clear: Humans can indeed move an asteroid. If we detect a dangerous space rock headed toward Earth, knocking it off course with a spacecraft is a potential option.

“You have lots of theories and ideas about ways that might potentially prevent an asteroid impact,” said Daly. “And for decades, they’ve just been that: theories and ideas. But now we can check the box and say that we know how to do this for real.”

DART demonstrated that a spacecraft can track down an asteroid and steer into it on its own, without ever having seen it before. At the moment of DART’s impact, transmissions traveling at the speed of light took 38 seconds to reach Earth, ruling out any real-time interventions from the ground. DART’s camera system, DRACO, fed images to a series of navigation algorithms that were able to identify Dimorphos and aim for the center of its lighted surface. The spacecraft scored a bulls-eye, smashing into Dimorphos just 25 meters (80 feet) away from where it was aiming.

“It’s really a testament to the engineers, to the folks who built the autonomous navigation here at APL,” said Andy Rivkin, who was a DART investigation team lead at the Johns Hopkins University Applied Physics Laboratory.

Rivkin also lauded the work that astronomers did to pinpoint where the asteroids would be 11 months after DART launched. “It’s getting DART to the right place, and knowing where the right place is,” he said.

From squished ball to watermelon

Although scientists heavily observed Dimorphos after DART’s impact, they don’t know exactly what happened on the asteroid’s surface. The answers will come in 2025, when the European Space Agency’s Hera mission arrives for a comprehensive follow-up survey. Scheduled to launch later this year, Hera will survey the aftermath of what happened in 2022.

One fact is already known: DART did so much damage that it actually changed Dimorphos’ shape. Around 1% of the asteroid’s mass was flung into space, forming the tail that scientists saw from the ground. The material in the tail is believed to have weighed around 10 million kilograms (22 million pounds), enough to fill about 60 rail cars.

All of that material streaming away from Dimorphos gave it a powerful shove that was 3.6 times stronger than the impact of DART itself.

“That is a key result from the DART mission,” said Daly. “The momentum enhancement contributed by the ejecta really does give you an extra push beyond what the spacecraft itself provides.”

Still more material resettled elsewhere on Dimorphos. The result of all this mayhem actually reshaped the asteroid: Before impact, it was shaped like a symmetrical, squished ball. After impact, it resembles an oblong watermelon.

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