[aetherson]

There'd have to be so much of it that we'd see it. There's way more dark matter than normal matter in the universe (stipulating that dark matter theories as we currently understand them are at a coarse level correct).

If it were "dark dust," there would be enough of it that we would be able to detect it through means other than gravitational ones.

[mixmastamyk]

Thanks. Given that the Oort cloud is very sparse and we can't see it, and we can't (optically) see even the largest planets on other stars, why would we expect to be able to see it?

[teraflop]

The objects we know of are orders of magnitude too small to explain the missing mass. The Oort cloud is estimated to make up about 0.002% of the solar system's mass. If instead it was 5 times more massive than everything else put together (which would be required for it to make up our solar system's share of the galaxy's dark matter) it would be a lot more visible.

[dalke]

For what it's worth, https://en.wikipedia.org/wiki/List_of_directly_imaged_exopla... is a list of the directly observed extrasolar planets.

[mtrpcic]

There's one other thing that goes against the idea of "dark dust". if it was "dark dust" that was just a sparse cloud of standard elements, we would be able to detect the makeup of the cloud by pointing a Spectrometer at some of the darker (but seemingly "denser") parts of the cloud to detect what it's made of.