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Rogue asteroids, to put it simply, are a threat to Earth. Although there hasn’t been a cataclysmic event in about 65 million years, that doesn’t mean there haven’t been any nail-biting moments during space rock flybys – in 2013, for example, the Chelyabinsk asteroid crashed into Earth’s atmosphere “burning as second sun” and send shock waves through the surrounding area.
Space agencies around the world understandably want to be prepared. To that end, NASA launched the Double Asteroid Redirection Test (DART) spacecraft in 2022, its first mission dedicated to demonstrating asteroid deflection through kinetic impact. DART successfully collided with a near-Earth asteroid called Dimorphos, which is part of a binary system because it orbits a larger asteroid called Didymos. We’ve already gotten a lot of incredible information from this impact, and we just got a little more. According to a paper published this year about the event, DART created a large crater in Dimorphos, reshaping the rock so much that it was forced out of its original progression.
“For the most part, our original predictions about how DART would change the way Didymos and its moons move in space were correct,” Derek Richardson, professor of astronomy at the University of Maryland and leader of the DART investigation work group, said in a statement. “But there are some unexpected results that help provide a better picture of how asteroids and other small bodies form and evolve over time.”
One surprise was how much DART was able to change Dimorphos. Before the collision, the asteroid was oblate, meaning it was slightly flattened or flattened along one axis, probably due to its own rotation or gravitational effects.
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After the collision, the shape of Dimorphos became prolate, meaning that the asteroid was stretched along its axis, making it longer in one direction. This elongation was probably caused by the impact by redistributing the mass of the asteroid and changing its rotational dynamics.
“We expected that Dimorphos would be a pre-impact prolate simply because that in general as we believed that the central lunar body would gradually accumulate material lost from a primary body like Didymos. It would normally be The natural formation of an elongated body would always point its long axis towards the main body,” explained Richardson. “But this result contradicts that idea and shows that something more complex is at work here. Furthermore, the impact-induced change in the shape of Dimorphos likely changed the way the he with Didymos.”
The DART collision did indeed disrupt the dynamics and balance of the two parts of the targeted binary system, shortening the entire orbit of Dimorphos, just as scientists had hoped.
“At first, Dimorphos was probably in a very relaxed position and had one side pointing towards the main body, Didymos, just as the Earth’s moon has one face pointing towards our planet,” Richardson explained. . “Now, it’s broken out of alignment, meaning it could wobble back and forth in its orientation. Dimorphos could also be ‘tumbling’, meaning it could be the reason why it would turn chaotically and unpredictably.”
The scientists also noted that the shape of Didymos remained unchanged, suggesting that the asteroid is more structurally stable and resilient enough to maintain its form.
The team is now waiting to find out when the debris will clear from the system, whether Dimorphos is still drifting in space and when (or if) the object will eventually regain its previous stability.
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“One of the biggest questions we have now is whether Dimorphos is stable enough to land spacecraft and install more research equipment on it,” he said. “It could take a century to see significant changes in the system, but it’s only been a few years since the impact. Learning about how long it takes Dimorphos to regain its stability tells us important things about its internal structure, which in turn informs future efforts to deflect hazardous asteroids.”
Those findings will have important implications for future missions, including the European Space Agency’s follow-up flight to the Didymos system in October 2024.
“DART has given us insight into complex gravitational physics that you can’t do in a lab, and all this research helps us calibrate our efforts to protect Earth in the event of an actual threat,” Richardson said. “There is a nonzero chance that an asteroid or comet will approach and threaten the planet. Now, there is an additional line of defense against these types of external threats.”
The paper was published on 23 August in The Planetary Science Journal.
