“Our original pre-impact predictions about how DART would change the way Didymos and its moon move through space were largely correct,” said Derek Richardson, a professor of astronomy at the University of Maryland and leader of the DART research working group. “But there are some unexpected findings that help provide a better picture of how asteroids and other small bodies form and evolve over time.”

The article published in Planetary science magazine On August 23, 2024, a team led by Richardson detailed remarkable observations after the impact and described potential implications for future asteroid research.

One of the biggest surprises was how much the DART impact changed Dimorphos’ shape. According to Richardson, the asteroid moon was originally oblate (shaped like a hamburger), but became more prolate (stretched out like a football) after the DART spacecraft collided with it.

“We expected Dimorphos to be prolate before the impact, simply because we thought that this is how a moon’s central body would gradually accumulate material shed from a primary body like Didymos. It would naturally tend to form an elongated body with its long axis always pointing toward the main body,” Richardson explained. “But this result contradicts that idea and suggests that there is something more complex going on here. Furthermore, the impact-induced change in Dimorphos’ shape has likely changed the way it interacts with Didymos.”

Richardson noted that although DART only hit the moon, the moon and the main body are gravitationally bound. The debris scattered by the spacecraft upon impact also played a role in disrupting the equilibrium between the moon and its asteroid, causing Dimorphos’ orbit around Didymos to shorten. Interestingly, Didymos’ shape remained the same — a finding that suggests the body of the larger asteroid is solid and rigid enough to retain its shape even after it lost mass to create its moon.

According to Richardson, the changes to Dimorphos have important implications for future exploration activities, including the European Space Agency’s follow-up mission to the Didymos system planned for October 2024.

“Originally, Dimorphos was probably in a very relaxed state and had one side facing the main body, Didymos, just as Earth’s moon always has one side pointing towards our planet,” Richardson explained. “Now it’s been knocked out of alignment, meaning it could be wobbling back and forth in its orientation. Dimorphos could also be ‘tumbling’, meaning we’ve made it rotate chaotically and unpredictably.”

The team is now waiting to see when the ejected debris will clear from the system, whether Dimorphos is still tumbling through space, and when it will eventually become stable again.

“One of our biggest questions now is whether Dimorphos is stable enough for spacecraft to land and install more research equipment,” he said. “It could take a hundred years before we see any noticeable changes in the system, but it’s only been a few years since the impact. Knowing how long it takes for Dimorphos to stabilize again will tell us important things about its internal structure, which in turn will impact future efforts to deflect dangerous asteroids.”

Richardson and his team hope that Hera will provide more information about DART’s impact. In 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, providing 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 that 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 come close and endanger the planet. Now we have an extra line of defense against those kinds of external threats.”