The Double Asteroid Redirection Test (DART) was a spacecraft that impacted the asteroid Dimorphos in 2022. The huge plume of debris that this created tripled the impact of that blow.
In 2022, NASA sent a spacecraft to crash into an asteroid to move it. With success: the impact had a greater effect on the asteroid’s orbit than predicted. Five articles in Nature of an analysis by the collision and the aftermath to leave now see why.
A big success
DART shot a spacecraft at the small asteroid Dimorphos, which orbits the larger asteroid Didymos. Five groups of researchers have focused on different aspects of the impact. The impact brought Dimorphos closer to Didymos, shortening its orbital period by about 33 minutes. That was 25 times the minimum change at which the mission would have been considered a success.
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That was possible because DART was right on target. “The spacecraft hit Dimorphos very close to the center, which is exactly where you want to hit the asteroid to maximize momentum transfer,” says astronomer Caroline Ernst from Johns Hopkins University in Maryland.
Extra push
But perhaps more importantly, after the impact, debris from the asteroid flew away, giving it an extra push. “People may see the DART mission as a fairly simple experiment, akin to playing billiards in space: a spacecraft collides with a massive asteroid,” says astronomer Cristina Thomas from Northern Arizona University. ‘but asteroids are much more than ‘just’ solid rocks.’
Most asteroids — including Dimorphos, it turns out — are mounds of debris held together weakly by gravity. So when DART hit Dimorphos, between 0.3 and 0.5 percent of its mass blasted off in a large plume of debris. This enhanced the momentum transfer from the spacecraft to the asteroid by a factor of 3.6.
If we ever need to use something like DART to deflect an asteroid heading for Earth, understanding that extra push is crucial. “The debris plume gives the asteroid a greater push than the spacecraft itself. That means that in the future, if we need to use this technology to deflect an asteroid, we don’t necessarily need a huge spacecraft,” says astronomer Jian Yang Li from the Planetary Science Institute in Arizona.
Active asteroids
The debris plume also places Dimorphos in a special category of asteroids called active asteroids, which have tails like comets. It has long been thought that these tails can form from collisions with smaller space rocks. DART has shown that idea to be correct. ‘We can now really check what happens to active asteroids. That helps to figure out what they’re made of, which takes us back to the origin of the solar system, when they formed,” says astronomer Ariel Graykowski from the SETI Institute in California.
After DART, we know we can change the orbit of a small asteroid like Dimorphos, but asteroids are so diverse that we’re not sure a similar mission would work on anything that comes our way. “I think the best way to apply this new knowledge is to do it again, but with something bigger,” says Graykowski. ‘We now know how fragile the asteroid ultimately was, so how much debris came off it, and how much it moved. We should use that to replicate it on a much larger scale.’