Asteroid is a ‘completely different body’ after being hit by NASA spacecraft, scientists say

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When NASA’s Double Asteroid Redirection Test spacecraft deliberately collided with the asteroid Dimorphos in September 2022, the impact may have caused “global deformation” of the space rock, according to new research.

The purpose of the DART mission was to conduct a full test of asteroid deflection technology for planetary defense and to see if a kinetic impact – such as crashing a spacecraft into an asteroid at a speed of 13,645 miles per hour (6.1 kilometers per second) – would be enough to change the motion of a celestial body in space.

Dimorphos is a moon-shaped asteroid orbiting a larger parent planet known as Didymos. Neither poses a threat to Earth, but the twin asteroid system was a perfect target to test the deflection technology because Dimorphos’ size is comparable to that of asteroids that could pose a threat to Earth.

Since the day of impact, astronomers have used data from ground-based telescopes to determine that the DART spacecraft reduced the orbital period of Dimorphos (or how long it takes to make a single revolution around Didymos) by about 32 to 33 minutes has changed. But another crucial piece of information needed to understand how to deflect asteroids that may be on a collision course with Earth in the future is the composition of space rocks.

Different types of asteroids that pose a threat – whether they are hard, stony asteroids or debris piles, which are essentially loose piles of rock held together by gravity – would require different deflection techniques.

The DART mission ended after a collision, but before the spacecraft collided with Dimorphos, the spacecraft provided an incredibly detailed view of the small asteroid’s boulder-covered surface, helping researchers learn more about how the space rock formed.

Astronomers were also able to make follow-up observations with ground-based and space-based telescopes, and with the Italian LICIACube satellite that closely tracked the DART mission and imaged the aftermath for 5 minutes and 20 seconds.

The observations showed that the impact sent a gigantic plume of material into space.

Now researchers have taken the research one step further by putting all this data into software to help answer important remaining questions, such as determining how the asteroid responded to the collision and what kind of crater was left behind.

Rather than forming a simple crater on Dimorphos, the DART impact reshaped the entire asteroid, the results suggest. A study describing the findings was published Monday in the journal Nature Astronomy.

The findings could prepare astronomers for what they will find when future missions fly past Dimorphos to better understand the effects of asteroid deflection technology.

Recreating the DART impact

A team of researchers modeled the impact using the Bern hydrodynamics shock physics code for smooth particles to achieve their results.

It is “a computer tool designed to simulate impact events. Shock physics codes in general are essential in 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 in the Department of Space Research and Planetary Sciences. sciences at the Physics Institute 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 impactor 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 did have, while varying factors they didn’t know, “such as the degree to which the boulders are stacked on top of each other , their density, the porosity of the material and its general cohesion. We also made some reasonable assumptions based on the physical properties of meteorites similar to Dimorphos,” Raducan said.

After running their simulations, the team focused on the one that most closely matched the original DART data.

The results indicated that Dimorphos is a mess made of rocky material from the asteroid Didymos, held together by weak gravity.

“On Earth, gravity is such that cratering occurs briefly, creating a typical crater cone angle of about 90 degrees,” says co-author Dr. Martin Jutzi from the Physics Institute of the University of Bern, who is also co-chair of the Hera Impact Physics. Working group, in a statement. “What we saw at DART’s Dimorphos impact was a much wider ejection cone angle extending up to 160 degrees, mainly influenced by the curved shape of the asteroid’s surface. And the crater just kept expanding because both gravity and material cohesion are so low.”

As a result, the crater essentially grew into the entirety of Dimorphos, completely changing the asteroid’s shape.

The Hera mission

Raducan and Jutzi are part of the research team participating in the European Space Agency’s Hera mission, which will launch a spacecraft in October on a journey to observe the aftermath of the DART impact, arriving in late 2026. Together with a pair of CubeSats, the mission will study the composition and mass of Dimorphos and how it was transformed by the impact, and determine how much momentum was transferred from the spacecraft to the asteroid.

“Our simulations suggest that the original flying saucer shape on the impact side of Dimorphos has been blunted: if you thought Dimorphos looked like a chocolate M&M at first, it now looks like a bite has been taken out of it!” Raducán 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 learn more about the transformative event.

The team believes that 1% of Dimorphos’s total mass was ejected into space by the impact, while 8% of the asteroid’s mass was shifted.

“Hera probably won’t be able to find any craters left by DART,” Raducan said. “What it will discover instead will be a completely different body.”

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