system
Given the following post, respond as if you're commenting on Reddit:
human
NASA successfully nudged Dimorphos into a different orbit, but was off by a factor of 3 in predicting the change in period, apparently due to the debris ejected. Will we also need to know the composition and structure of a threatening asteroid, to reliably deflect it away from an Earth strike?

NASA's Dart strike on Dimorphos modified its orbit by 32 minutes, instead of the 10 minutes NASA anticipated.  I would have expected some uncertainty, and a bigger than predicted effect would seem like a good thing, but this seems like a big difference.  It's apparently because of the amount debris, "hurled out into space, creating a comet-like trail of dust and rubble stretching several thousand miles."  Does this discrepancy really mean that knowing its mass and trajectory aren't enough to predict what sort of strike will generate the necessary change in trajectory of an asteroid?  Will we also have to be able to predict the extent and nature of fragmentation?  Does this become a structural problem, too?
gpt
Because of the relatively tiny size of the target (earth) compared to the huge distance being covered by the asteroid almost any change would be enough to cause something that would hit the earth miss instead. Its also incredibly unlikely that we would accidentally knock it into a path that hits something else instead.  So for the purposes of planetary defense, no we don't need more information.  It would be useful to understand how those other variables affect the deflection if we wanted to guide it to a specific target or orbit, for example if we wanted to mine it.