"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 and a DART investigation working group lead. "But there are some unexpected findings that help provide a better picture of how asteroids and other small bodies form and evolve over time."

Published in the 'Planetary Science Journal' on August 23, 2024, the study led by Richardson highlights significant post-impact observations and explores their implications for future asteroid research.

One of the study's most surprising findings was the extent of the change in Dimorphos' shape. Initially oblate, resembling a hamburger, the asteroid moon became more prolate, or football-shaped, after the collision with DART.

"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. It would naturally tend to form an elongated body that would always point its long axis toward the main body," 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."

Although DART only impacted Dimorphos, the gravitational connection between the moon and Didymos meant that the debris scattered by the impact also affected the system. The result was a shortened orbit for Dimorphos around Didymos, while the shape of Didymos itself remained unchanged-a sign of its firm and rigid structure.

According to Richardson, these changes in Dimorphos have significant implications for upcoming space missions, including the European Space Agency's Hera mission, which is set to visit the Didymos system in 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 explained. "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 observing to see when the ejected debris will clear, if Dimorphos is still tumbling, and when it will regain stability.

"One of our biggest questions now is if Dimorphos is stable enough for spacecraft to land and install more research equipment on it," he said. "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."

The team hopes the Hera mission will offer more insight into DART's impact. By late 2026, Hera will reach the Dimorphos-Didymos binary system to analyze the internal properties of both asteroids, offering a more detailed evaluation of the DART mission and its future implications.

"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," Richardson said. "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."

Research Report:The Dynamical State of the Didymos System before and after the DART Impact

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