NASA's asteroid-smashing DART mission 'completely reshaped' its target Dimorphos, scientists say

NASA’s DART mission was the first test of a planetary defence system designed to prevent a potential doomsday meteorite collision with Earth. (Supplied: NASA/Johns Hopkins APL)

NASA’s successful mission to smash a spacecraft into a small asteroid moon in 2022 is likely to have “completely reshaped” its target, according to new research.

Here’s what scientists believe happened, what it tells us about the moonlet known as Dimorphos, and what Europe’s Hera mission is likely to find when it travels there in the coming years.

Earth’s first planetary defence system test

NASA’s Double Asteroid Redirection Test (DART) intentionally directed a spacecraft into the path of Dimorphos, a tiny moonlet of near-Earth asteroid Didymos, in September 2022.

The moonlet wasn’t a threat to Earth, so it was used as the first opportunity to test a planetary defence system using the “kinetic impact technique” — which is essentially slamming a spacecraft into an asteroid.

The table-sized craft crashed into Dimorphos at a speed of around 22,530 kilometres per hour (6.2 kilometres per second).

An image captured two days after the initial impact showed a trail of debris more than 10,000 kilometres long, made up of dust and other material from the impact.

The successful collision helped scientists who were working on preventing potential doomsday meteorite collisions with Earth.

The mission shifted Dimorphos’s trajectory and shortened its orbit around Didymos by 33 minutes, giving researchers an idea of how effective a similar technique would be for other asteroids and meteorites.

Dimorphos likely ‘completely reshaped’ by impact

The latest research published in Nature suggests the DART impact might not have created a small impact crater on Dimorphos, but actually reshaped the moonlet in its entirety, in a process known as global deformation.

A team of scientists, led by experts at the University of Bern in Switzerland, say this process “caused resurfacing of Dimorphos with material from its interior”.

They estimate only 1 per cent of Dimorphos’s mass was thrown into space by the impact, while around 8 per cent of its mass was shifted around its body.

Here’s an animation showing what the researchers believe Dimorphos looked like for the first 30 minutes after impact:

Lead researcher Sabina Raducan says:

“The likelihood is that the crater grew to encompass the entire body itself, so that Dimorphos ended up being completely reshaped.”

The results indicate Dimorphos is “potentially a weak rubble pile made up of material shed from its asteroid Didymos” and pulled together by gravity, the researchers say.

Help from computers and Queen’s Brian May

The scientists created simulations of the DART impact using a computer model that had been developed over two decades.

Ms Raducan says these simulations took quite a lot of time.

“This is a computationally intensive process, with each simulation taking around a week and a half to run, and we ran around 250 simulations overall, reproducing the first two hours after impact,” she says.

“Then what we did is check which of the simulation run outcomes most closely match observed reality.

“The results indicate that Dimorphos is a relatively weak ‘rubble pile’ asteroid, held together by the asteroid’s extremely weak gravity rather than cohesive strength.

“This helps to account for the unexpectedly high efficiency of DART’s orbital deflection.”

This animation shows a computer simulation of the moment 178 seconds after impact:

To help interpret the results of their simulations, the researchers also “made use of stereoscopic images” prepared by Queen guitarist and astrophysicist Sir Brian May and his collaborator Claudia Manzoni.

The scientists say their results suggest that similarly formed asteroid moons “are easily reshaped and their surfaces are relatively young”.

They say their findings will help with future asteroid deflections, and “provide valuable information for understanding the formation and characteristics” of similar asteroids.

Study suggests Hera won’t find a crater

The European Space Agency (ESA) is preparing to launch its own planetary defence probe Hera in October 2024, which will travel to Dimorphos to study the impact of NASA’s DART mission.

But the study led by the University of Bern suggests no crater will be found by Hera, which will likely find a completely remodelled version of Dimorphos instead.

The craft is expected to carry out a detailed post-impact survey of the moonlet, looking at how the entire asteroid reacted to the impact and how efficiently the DART spacecraft transferred its momentum.

Hera is scheduled to arrive at Dimorphos at the end of 2026.