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When NASA’s Double Asteroid Redirect Test spacecraft intentionally crashed into the asteroid Dimorphos in September 2022, the impact may have caused a “global deformation” of the space rock, according to new research.
The goal of the DART mission was to conduct a full-scale test of asteroid deflection technology for planetary defense and see if there is a kinetic impact – like slamming a spacecraft into an asteroid at 13,645 miles per hour (6.1 kilometers per second). – it was enough to change the movement of a celestial object in space.
Dimorphos is a moonlet asteroid that orbits a larger parent asteroid called Didymos. Not a threat to Earth either, but the binary asteroid system was an ideal target for testing deflection technology because the size of Dimorphos is comparable to asteroids that could pose a threat to Earth.
Since the day of impact, astronomers have used data from a ground-based telescope to determine that the DART spacecraft changed the orbital period of Dimorphos — or how long it takes to make one revolution around Didymos — by about 32 to 33 minutes. But another critical piece of information needed to understand how to deflect asteroids that may be on a potential collision course with Earth in the future is the composition of space rocks.
Different types of threat asteroids — whether hard asteroids, rocks or piles of rubble, which are effectively loose piles of rock held together by gravity — would require different deflection techniques.
The DART mission ended with an impact, but before it collided with Dimorphos, the spacecraft transmitted an incredibly detailed view of the small boulder-covered asteroid’s surface that is helping researchers learn more about how the space rock formed.
Astronomers were also able to make follow-up observations with ground and space-based telescopes, and with the Italian satellite LCIACube which briefly followed the DART mission and imaged the result for 5 minutes and 20 seconds.
The observations showed that the impact released a huge debris of material into space.
Now, researchers have taken the investigation a step further by entering all this data into software to help answer important remaining questions, such as determining how the asteroid responded to the collision and what a type of crater that was left.
Rather than creating a simple crater on Dimorphos, the impact of DART has reshaped the entire asteroid, the results suggest. A study that described the results appeared Monday in the journal Nature Astronomy.
The results could prepare astronomers for what they will find when future missions fly with Dimorphos to better understand the effects of asteroid deflection technology.
Recreating the impact of DART
A team of researchers modeled the impact using the Bern smoothed particle hydrodynamics shock physics code to arrive at their results.
It is a “computational tool designed to simulate impact events. Shock-physics codes are essential in general for the study of collisions and impact processes. They incorporate various models, including material models and porosity models, to accurately represent the physical conditions during hypervelocity impact events, such as high pressures and temperatures,” said lead study author Dr. Sabina Raducan, postdoctoral researcher at the space and planetary research department. sciences at the Institute of Physics of the University of Bern in Switzerland.
The software has been validated by replicating other impacts, including when Japan’s Hayabusa2 spacecraft slammed a small copper collider into the Ryugu asteroid in 2019.
The team ran 250 simulations to recreate the first two hours after the DART impact based on the data they had while varying factors they didn’t know, “like how closely packed boulders were, their density, the porosity of the material and its overall cohesion. We also made some reasonable assumptions based on the physical properties of meteorites like Dimorphos,” said Raducan.
After running their simulations, the team focused on the closest match to the original DART data.
The results indicated that Dimorphos is a pile of rubble made of rocky material shed from the asteroid Didymos, held together by weak gravity.
“On Earth the force of gravity is so great that cratering occurs briefly, producing a typical cratering cone angle of about 90 degrees,” said study co-author Dr. Martin Jutzi from the Institute of Physics of the University of Bern, who is also co-chair of Hera Impact Physics. Working Group, in a statement. “What we saw with the DART impact on Dimorphos was a much wider ejecta cone angle extending up to 160 degrees, which was mainly influenced by the curved shape of the asteroid’s surface. And the crater continued to expand, because the gravity and material cohesion is so low.
As a result, the crater essentially grew to contain all of the Dimorphos, completely changing the shape of the asteroid.
Hera’s mission
Raducan and Jutzi are part of the investigation team participating in the European Space Agency’s Hera mission, which will send a spacecraft in October on a journey to observe the aftermath of the DART impact, coming near the end of 2026. Together with a pair of CubeSats, will the mission to study the composition and mass of Dimorphos and how it was transformed by the impact and will determine how much momentum was transferred from the spacecraft to the asteroid.
“Our simulations suggest that Dimorphos had its initial flying saucer shape on the impact side: if you thought Dimorphos was like a chocolate M&M from the beginning, now it looks like it’s been bitten!” Raducan said.
Queen guitarist and astrophysicist Sir Brian May, along with his collaborator, chemical engineer and materials researcher Claudia Manzoni, also shared stereoscopic images to help the team determine more about the reshaping event.
The team believes the impact ejected 1% of Dimorphos’ total mass into space, while 8% of the asteroid’s mass was moved around.
“Hera probably won’t be able to find any craters left by DART,” Raducan said. “What he will discover instead is a very different body.”
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