This was the focus of an exciting new study by researchers Harrison Agrusa and Camille Chatenet from Université Côte d’Azur, France. They pointed out unanticipated shifts in the orbital period of Dimorphos, one of the small moons in the Didymos system. NASA’s Double Asteroid Redirection Test (DART) mission swung for the fences. As expected, the orbital period of Dimorphos was shortened by roughly 33 minutes. This change request included an unanticipated 30 second decrease due to the effect.
The DART mission aimed to test asteroids deflection technique. It provided an irreplaceable opportunity to witness the effects of this revolutionary event. Agrusa and Chatenet’s study focused on understanding the mechanisms behind the abrupt changes in Dimorphos’s orbital dynamics. Their findings suggest that gravitational scattering of ejecta from the impact cannot explain the observed decrease in orbital period. They provide different explanations for this puzzling trend.
Dimorphos didn’t have enough gravitational force to scatter material efficiently. Its estimated Safronov number of less than 0.14 indicates that it would not have been able to produce enough angular momentum to trigger the substantial changes we see. To investigate this further, the researchers simulated the motion of 10,000 ejecta particles. Their goal was to understand the collective behavior of these particles in the wake of the DART impact.
What we found was a curious boomerang effect. Instead of flying off in all directions from Dimorphos, a great deal of material came back together and reformed in the system post-collision. This finding goes against prior assumptions on how such impacts affect orbits and shows the dramatic intricacies at play with asteroid dynamics.
The full study can now be found on arXiv and DOI 10.48550/arxiv.2509.20197. Furthermore, a complementary study along the same lines can be found at DOI 10.1051/0004-6361/202555772. This research carries important implications. A post on Science X Network cites these findings, sparking ongoing debates on asteroid impact dynamics and their possible utilization in planetary defense strategies.