A recent study sheds light on the geophysical processes related to the formation and development of asteroids.
In 2022, NASA’s Double Asteroid Redirection Test (DART) spacecraft collided with an asteroid moon named Dimorphos. This impact significantly altered the moon’s structure, resulting in a large crater and changing its shape so much that it disrupted its natural evolutionary path. Researchers believe that Dimorphos might begin to “tumble” erratically as it tries to regain gravitational balance with its parent asteroid, Didymos.
“Overall, our initial predictions about how DART would affect the motion of Didymos and its moon in space turned out to be largely correct,” stated Derek Richardson, an astronomy professor at the University of Maryland and a lead member of the DART investigation team. “However, some unexpected results offer a clearer understanding of how asteroids and other small celestial objects form and change over time.”
The research, published in Planetary Science Journal on August 23, 2024, by Richardson and his team, highlighted important observations following the impact and discussed their implications for future asteroid studies.
A significant surprise was the degree to which DART altered Dimorphos’s shape. Richardson noted that prior to the impact, the asteroid moon was oblate (which looks like a hamburger), but after the collision, it became more prolate (similar to a stretched football).
“We anticipated that Dimorphos would be prolate before the impact because we thought that’s how a moon’s central body would gradually gather material released from its primary body, Didymos. The elongated shape would naturally align its long axis toward the main body,” Richardson elaborated. “This unexpected finding implies a more complicated process is at play. Additionally, the change in Dimorphos’s shape from the impact likely altered its interactions with Didymos.”
Richardson explained that even though DART only struck Dimorphos, the gravitational connection between the moon and Didymos means that the debris from the impact influenced their equilibrium, causing Dimorphos’s orbit around Didymos to shorten. Interestingly, Didymos itself maintained its shape, suggesting that the larger asteroid is solid and sturdy enough to retain its structure despite losing mass to form its moon.
According to Richardson, these changes in Dimorphos could significantly impact future exploration missions, including the European Space Agency’s follow-up project to the Didymos system set for October 2024.
“Before the impact, Dimorphos was likely in a stable state, consistently showing one side to Didymos, similar to how Earth’s moon always faces our planet,” Richardson pointed out. “Now, it is misaligned, which could lead to it wobbling in different directions. Dimorphos might even be ‘tumbling,’ which means it could be rotating unpredictably and chaotically.”
The research team is currently monitoring when the released debris will dissipate, whether Dimorphos is still tumbling, and when it might return to its prior stability.
“A key question for us is whether Dimorphos is stable enough for spacecraft to land and deploy additional research instruments on it,” he said. “While it could take a hundred years to observe significant changes in the system, only a few years have passed since the impact. Understanding how long it takes for Dimorphos to regain stability is crucial for learning about its internal structure, which will inform future efforts to deflect potentially hazardous asteroids.”
Richardson and his team are hopeful that the Hera mission will yield further insights regarding the effects of DART’s impact. Hera is expected to reach the binary asteroid system consisting of Dimorphos and Didymos by late 2026, allowing for a first-time assessment of both asteroids’ internal characteristics and a more comprehensive analysis of the DART mission and its future implications.
“DART has provided us with valuable knowledge about complex gravitational physics that can’t be replicated in a lab, and all this research aids us in fine-tuning our efforts to protect Earth against actual threats,” Richardson remarked. “There is a genuine possibility that an asteroid or comet could pose a danger to our planet. We now have an additional layer of defense against such external risks.”
