On September 26, 2022, NASA’s Double Asteroid Redirection Test (DART) spacecraft successfully deflected the 170-meter-wide asteroid Dimorphos, proving the effectiveness of asteroid deflection tactics. However, a new study by a group of scientists reveals that the impact not only altered Dimorphos’ orbit but also significantly changed its shape.

Before the collision, Dimorphos was known to have a roughly symmetrical shape, resembling a squished ball this is wider than it is tall. The asteroid completed one orbit around its host asteroid Didymos in approximately 11 hours and 55 minutes. However, following DART’s impact, Dimorphos’ orbit became non-circular, with an orbital period of 33 minutes and 15 seconds shorter. Additionally, the shape of the asteroid transformed from a symmetrical object to a “triaxial ellipsoid,” similar to an oblong watermelon.

To understand these changes, the scientists utilized computer models and data from three sources. The first source was images captured by DART’s Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO) camera, which allowed for close-up measurements of both Didymos and Dimorphos before the impact. The second data source was the Goldstone Solar System Radar, which measured the position and velocity of Dimorphos. The third and most significant data source was ground telescopes that observed the changes in the asteroids’ light curves over time.

The study’s models showed that DART’s impact caused Dimorphos to rock back and forth as it orbits around Didymos. Immediately after the impact, Dimorphos’ orbital period shortened by 32 minutes and 42 seconds, making it 11 hours, 22 minutes, and 37 seconds in total. As the asteroid continuously lost surface material into space, its orbital period decreased further, finally settling at around 11 hours, 22 minutes, and three seconds. Overall, the impact altered the asteroid’s orbit by 33 minutes and 15 seconds, bringing Dimorphos 37 meters closer to Didymos.

The findings provide insights into the nature of asteroids. Dimorphos is believed to be a loosely-packed “rubble pile” asteroid, similar to asteroid Bennu, which was studied by NASA’s OSIRIS-REx mission. The European Space Agency’s upcoming Hera mission will investigate the long-term changes brought about by DART’s impact.

The study’s results have been published in the Planetary Science Journal. Tom Statler, NASA’s lead scientist for solar system small bodies, emphasizes that the outcome of this research aligns with other studies, demonstrating a solid scientific result. He notes that DART not only showcases a pathway for asteroid-deflection technology but also enhances our understanding of asteroids and their behavior.

This groundbreaking mission and its subsequent findings mark a significant step forward in our ability to protect Earth from potential asteroid threats. With further exploration and analysis, scientists and engineers can continue to improve our understanding and develop effective strategies for defending our planet against future asteroid impacts.

Image Credit: NASA/JPL-Caltech