In a successful test dubbed “picture perfect,” NASA’s Double Asteroid Redirection Test (DART) accomplished its mission of colliding a car-sized spacecraft into an asteroid in September 2022. The mission’s objective was to demonstrate the capability of diverting a hazardous space rock from Earth despite the relatively low probability of such a cataclysmic event. The impact of DART not only altered the orbit of the targeted asteroid but also, as revealed in a study published in the Planetary Science Journal on March 19, likely modified its shape.
The focus of DART was the asteroid Dimorphos, measuring 560 feet wide, which orbits a giant near-Earth asteroid known as Didymos. Before the collision, Dimorphos possessed a symmetrical oblate spheroid shape. However, the impact of DART induced significant changes, leading to what Shantanu Naidu, a co-author of the study and navigation engineer at NASA’s Jet Propulsion Laboratory (JPL), described as a transition from a relatively symmetrical object to a “triaxial ellipsoid,” akin to an elongated watermelon.
Before the collision, Dimorphos completed one orbit around Didymos in approximately 11 hours and 55 minutes, maintaining a well-defined, circular orbit around 3,900 feet from it. Following the impact, the orbital period of Dimorphos was shortened by approximately 33 minutes and 15 seconds.
Naidu and the research team utilized various data sources to analyze the aftermath of the collision in their computer models. These included images captured by DART as it approached the asteroid, providing detailed measurements of the gap between Didymos and Dimorphos. Additionally, data from NASA’s Deep Space Network’s Goldstone Solar System Radar near Barstow, California, facilitated precise measurements of Dimorphos’ position relative to Didymos post-impact.
The study also relied on observations from ground telescopes worldwide, which monitored the light curve of both asteroids, reflecting changes in sunlight off their surfaces over time. By comparing the light curves before and after the collision, the researchers gained insights into how DART altered Dimorphos’ motion and orbit.
According to the findings, Dimorphos’ orbit became slightly elongated or eccentric post-impact, evidenced by subtle timing differences in mutual events with Didymos. The precision of the models allowed for detecting slight oscillations in Dimorphos’ orbit as it orbited Didymos.
Furthermore, the models determined that DART’s impact reduced the average distance between the two asteroids, thereby initially shortening Dimorphos’ orbital period by approximately 32 minutes and 42 seconds. Subsequent shedding of rocky material by Dimorphos further shortened its orbital period to 11 hours, 22 minutes, and 3 seconds per orbit, approximately 33 minutes and 15 seconds less than before the collision.
A study published in February suggested that Dimorphos is likely a loose rubble pile asteroid akin to asteroid Bennu, owing to its collision with DART. The consistency of these findings across independent studies underscores the significance of DART in advancing asteroid-deflection technology and deepening our understanding of asteroid composition and behavior, as noted by Tom Statler, lead scientist for solar system minor bodies at NASA Headquarters.
The European Space Agency’s Hera mission, scheduled to launch in October 2024, will provide further insights into Didymos and Dimorphos, potentially confirming the extent to which DART reshaped Dimorphos.
