NASA's DART mission altered not just the orbit but also the shape of the asteroid Dimorphos.
A study led by NASA's Jet Propulsion Laboratory (JPL) has revealed that the DART mission (Double Asteroid Redirection Test) not only changed the movement of the asteroid Dimorphos but also its form. The impact occurred on September 26, 2022, marking a significant milestone in demonstrating the capability to deflect a potentially hazardous asteroid.
The asteroid Dimorphos captured by NASA's DART mission two seconds before the spacecraft hit its surface on September 26, 2022. The observations before and after the impact suggest it is a loosely-packed "rubble pile" object.
Credit: NASA/Johns Hopkins APL
Before the impact, Dimorphos, which orbits a larger asteroid named Didymos, had an oblate spheroid shape, resembling a flattened ball. Its loop around Didymos, at a distance of about 3,900 feet, took 11 hours and 55 minutes.
"When DART struck, things got really interesting," says Shantanu Naidu, navigation engineer at JPL, who led the study. "Dimorphos's orbit is no longer circular: its orbital period" – the time needed to complete a single orbit – "is now reduced by 33 minutes and 15 seconds. And the entire shape of the asteroid has changed, transitioning from a relatively symmetrical object to a 'triaxial ellipsoid' – more elongated."
Computer modeling, backed by data collected by DART, NASA's Goldstone Solar System Radar, and ground-based telescopic observations, has clarified these changes. The impact not only shortened Dimorphos's orbit around Didymos but also changed its shape, transforming it into a more elongated object.
This orbital evolution shows a significant reduction in the average distance between the two asteroids, indicating that Dimorphos is now about 121 feet closer to Didymos than before the impact. These findings confirm that Dimorphos is a loosely-packed "rubble pile," a characteristic similar to asteroid Bennu.
The European Space Agency's (ESA) Hera mission, scheduled for October 2024, will visit the pair of asteroids to conduct a detailed study and confirm how DART has reshaped Dimorphos.
This study is not just a step forward toward asteroid deflection technology; it also offers a new fundamental understanding of asteroids and their behavior.