An illustration depicting NASA’s Double Asteroid Redirection Test (DART) spacecraft (DART) prior to impact at the Didymos binary asteroid system.
NASA’s DART (Double Asteroid Redirection Test) is believed to have permanently changed the shape and orbit of an asteroid moon when it impacted the asteroid. This is according to research from the University of Maryland that provides insights into the geophysics behind asteroid formation and evolution.
Remember movies like Armageddon from the 90s? That film was about how Bruce Willis and NASA saved the world from an asteroid that would have destroyed the Earth. Well, now DART may very well be able to do exactly that just by giving an asteroid a little push, thereby changing its directory away from Earth.
Asteroid moons are natural satellites that orbit asteroids. While most moons are associated with planets, some asteroids have their own moons, creating a fascinating and often unexpected celestial phenomenon.
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DART was the first-ever mission dedicated to investigating and demonstrating one method of asteroid deflection by changing an asteroid’s motion in space through kinetic impact. On Sept. 26, 2022, DART impacted the asteroid moonlet Dimorphos, a small body just 530 feet (160 meters) in diameter. It orbits a larger, 2,560-foot (780-meter) asteroid called Didymos.
“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.
The scientists said that one of the most unexpected findings was the significant alteration of Dimorphos’ shape following the DART impact. Initially a more rounded object, Dimorphos became noticeably more elongated after the collision.
“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.
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.
