"To detect dark matter, scientists have to wait for the extremely rare occasion when a dark matter particle knocks into an atomic nucleus in the detector and makes it vibrate"
Why? If dark matter is 90+% of the mass of 'everything', then surely many more anomalies would occur without us having to be hit by a chunk of dark matter. It would simply have to be anywhere near us (or a nearby body we could observe carefully) to observe weird gravitational effects. Nearby ones, not 'out there in other galaxies' ones.
Assuming it's not near us, why would that be? Our star isn't much affected by it. We can't see nearby stars being pulled willy-nilly. How far out must we search before we could reasonably assume it doesn't exist and there might be another explanation?
[edit] And if it's a weird non-localised 'blanket' that can't hit you in the foot, then it'd be great to have some guesses as to the structure so we can test for it. Does it exist inside all galaxies? Is it in the middle, or does it rotate like normal 'matter'? If it exists in the perimeter, is much heavier, and spins like visible matter, do we have to invent a super-ultra-dark matter to explain why common-or-garden dark matter doesn't fly off into space? If it's in the middle and clumpy, could it collapse into a dark-matter black hole, especially since there's no radiation to force particles apart? Is it only one particle type, or a family like visible matter? Since it has mass, is there another form it can convert to as visible mass does? Since it doesn't radiate (being dark) what happens to the energy when (if) it converts?
If it's clumpy, stop worrying about visible asteroids. It's the invisible ones that can really hurt you :)