Nobody wants to accidentally "disrupt" an asteroid, because those components can still head for Earth. As I often say, it's like turning a cannonball into a shotgun spray.
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This is chaotic, potentially very destructive—and if DART hit Dimorphos a little harder, it would have broken that asteroid too. You have to be very sure that when you hit an Earthbound asteroid, you are deflecting it, not fragmenting it.
The second reason DART isn't a silver bullet is that it did not give Dimorphos as much of a deflection as you think. Yes, the orbit shrank a lot. But you know how much Dimorphos actually moved?
I've often by told you need 10 years or more to build, plan and execute an asteroid deflection mission. This is because the deflection a kinetic impactor can give an Earthbound asteroid would be tiny. Only over time does the shifted orbit add up enough to ensure it'll miss Earth.
Yes, it's smaller than Dimorphos (YR4 is 40-90m), meaning it would need less of a deflection than a larger asteroid. But we aren't going to see it again until another Earth flyby in 2028. So much could go wrong if we try and hit it with something like DART.
It may be smaller, or larger. If it's too big, we may not be able to deflect it with one spacecraft. We'd need several to hit it perfectly, all without catastrophically breaking it.
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The change in velocity delivered by the impact was 2.7mm/s. https://www.llnl.gov/article/49541/study-looks-velocity-impact-asteroid-dimorphos