New study provides insights into the geophysics behind asteroid formation and evolution.
A University of Maryland-led study reveals new details about asteroid dynamics following NASA’s DART mission, which intentionally collided with the asteroid moon Dimorphos in 2022. The impact significantly altered Dimorphos’ trajectory and shape, leading to unexpected gravitational behaviors. These findings challenge previous assumptions about asteroid evolution and could influence future planetary defense strategies and space missions, as researchers continue to assess the system’s stability and potential for further exploration.
When NASA’s Double Asteroid Redirection Test (DART) spacecraft collided with an asteroid moon called Dimorphos in 2022, the moon was significantly deformed—creating a large crater and reshaping it so dramatically that the moon derailed from its original evolutionary progression—according to a new study. The study’s researchers believe that Dimorphos may start to “tumble” chaotically in its attempts to move back into gravitational equilibrium with its parent asteroid named Didymos.
Insights From DART’s Collision With Dimorphos
“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.”
The paper published in Planetary Science Journal on August 23, 2024, by a team led by Richardson detailed notable post-impact observations and described possible implications for future asteroid research.
Unexpected Changes in Asteroid’s Shape and Dynamics
One of the biggest surprises was how much the impact with DART changed the shape of Dimorphos. 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 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.”
Richardson noted that although DART only hit the moon, the moon and the main body are connected through gravity. The debris scattered by the spacecraft on impact also played a role in the disturbed equilibrium between the moon and its asteroid, shortening Dimorphos’ orbit around Didymos. Interestingly, Didymos’ shape remained the same—a finding that indicates that the larger asteroid’s body is firm and rigid enough to maintain its form even after losing mass to create its moon.
Implications for Future Space Missions
According to Richardson, Dimorphos’ changes have important implications for future exploration efforts, including the European Space Agency’s follow-up mission to the Didymos system slated 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 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.”
Stability and Future Research Opportunities
The team is now waiting to find out when the ejected debris will clear from the system, whether Dimorphos is still tumbling in space, and when it will eventually regain its previous 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.”
DART’s Role in Planetary Defense
Richardson and his team hope that Hera 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, 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 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.”
Reference: “The Dynamical State of the Didymos System before and after the DART Impact” by Derek C. Richardson, Harrison F. Agrusa, Brent Barbee, Rachel H. Cueva, Fabio Ferrari, Seth A. Jacobson, Rahil Makadia, Alex J. Meyer, Patrick Michel, Ryota Nakano, Yun Zhang, Paul Abell, Colby C. Merrill, Adriano Campo Bagatin, Olivier Barnouin, Nancy L. Chabot, Andrew F. Cheng, Steven R. Chesley, R. Terik Daly, Siegfried Eggl, Carolyn M. Ernst, Eugene G. Fahnestock, Tony L. Farnham, Oscar Fuentes-Muñoz, Edoardo Gramigna, Douglas P. Hamilton, Masatoshi Hirabayashi, Martin Jutzi, Josh Lyzhoft, Riccardo Lasagni Manghi, Jay McMahon, Fernando Moreno, Naomi Murdoch, Shantanu P. Naidu, Eric E. Palmer, Paolo Panicucci, Laurent Pou, Petr Pravec, Sabina D. Raducan, Andrew S. Rivkin, Alessandro Rossi, Paul Sánchez, Daniel J. Scheeres, Peter Scheirich, Stephen R. Schwartz, Damya Souami, Gonzalo Tancredi, Paolo Tanga, Paolo Tortora, Josep M. Trigo-Rodríguez, Kleomenis Tsiganis, John Wimarsson and Marco Zannoni, 23 August 2024, The Planetary Science Journal.
DOI: 10.3847/PSJ/ad62f5
This research was supported by NASA (Contract Nos. 80MSFC20D0004, 80NSSC22K1173, HST-GO-17292 and NAS 5-26555), U.S. National Science Foundation (Grant No. DGE 2040434), the Centre national d’études spatiales (CNES), the European Space Agency (ESA), the European Research Council, the Italian Space Agency, the Swiss National Science Foundation and the Grant Agency of the Czech Republic. This article does not necessarily reflect the views of these organizations.
Other UMD-affiliated DART research contributors and study co-authors include Astronomy Principal Research Scientist Tony Farnham, Astronomy Professor Douglas Hamilton, former aerospace engineering postdoctoral associate Yun Zhang and alums Harrison Agrusa (M.S. ’19, Ph.D. ’22, astronomy) and Stephen Schwartz (M.S. ’07, Ph.D. ’13, astronomy).
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