DART impact sent asteroid into a chaotic and unpredictable tumble

Upon the momentous collision of NASA’s Double Asteroid Redirection Test (DART) spacecraft with an asteroid moon named Dimorphos in 2022, the course of the celestial body’s evolution took an unexpected turn.

The impact left such a profound mark that the moon was rendered significantly deformed, creating a significant crater and reshaping its form to the point of derailment from its original path.

Scientists believe that the newly restructured Dimorphos might now be undergoing a chaotic “tumble” in its attempts to regain gravitational balance with its parent asteroid, Didymos.

The DART impact study

“For the most part, our original pre-impact predictions about how DART would change the way Didymos and its moon move in space were correct,” said Derek Richardson, a professor of astronomy at the University of Maryland.

“But there are some unexpected findings that help provide a better picture of how asteroids and other small bodies form and evolve over time.”

In a recent study published in the Planetary Science Journal, Richardson and his team describe significant post-impact observations and possible implications for future asteroid research.

Dimorphos: From hamburger to football

One of the biggest surprises was the degree to which the DART impact transformed the shape of Dimorphos.

According to Richardson, the asteroid moon, originally oblate like a hamburger, assumed a more prolate figure, comparable to a stretched football, after the collision.

“We were expecting Dimorphos to be prolate pre-impact simply because that’s generally how we believed the central body of a moon would gradually accumulate material that’s been shed off a primary body like Didymos,” Richardson explained.

“But this result contradicts that idea and indicates that something more complex is at work here. Furthermore, the impact-induced change in Dimorphos’ shape likely changed how it interacts with Didymos.”

Ripple effects of the DART impact

Richardson noted that despite the DART spacecraft impacting only the moon, the moon and the main asteroid remain interlinked through gravity.

The debris scattered by the impact of the spacecraft disturbed the equilibrium between the moon and the asteroid, resulting in a shorter orbit of Dimorphos around Didymos.

Interestingly, Didymos’ shape remained unchanged, suggesting that the larger asteroid’s body is sturdy and rigid enough to retain its shape even after losing mass to create its moon.

The future of asteroid deflection

The results of the DART impact hold significant ramifications for future exploration. The European Space Agency has planned a follow-up mission to the Didymos system for October 2024.

“Originally, Dimorphos was probably in a very relaxed state and had one side pointing toward the main body, Didymos, just like how Earth’s moon always has one face pointing toward our planet,” Richardson noted.

“Now, it’s knocked out of alignment, which means it may wobble back and forth in its orientation. Dimorphos might also be ‘tumbling,’ meaning that we may have caused it to rotate chaotically and unpredictably.”

The team is now waiting to find out when the ejected debris will clear from the system and when Dimorphos will regain its previous stability.

“It could take a hundred years to see noticeable changes in the system, but it’s only been a few years since the impact. Learning about how long it takes Dimorphos to regain its stability tells us important things about its internal structure, which in turn informs future attempts to deflect hazardous asteroids,” said Richardson.

A long-term defense strategy

Richardson and his team hope that Hera, the European Space Agency’s mission, will provide more information about DART’s impact.

By late 2026, Hera will arrive at the binary asteroid system containing Dimorphos and Didymos to assess the internal properties of both asteroids for the first time. This will provide a more detailed analysis of the DART mission and its implications for the future.

“DART gave us insight into complicated gravitational physics that you can’t do in a lab, and all of this research helps us calibrate our efforts to defend Earth in the event of an actual threat,” said Richardson.

“There’s a nonzero chance that an asteroid or comet will approach and endanger the planet. Now, we have an additional line of defense against these kinds of external threats.”

The study is published in the journal Planetary Science.

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