Interstellar Interlopers, Coming in from the great beyond Options

[Holder of the Tw...]

They finally found a chunk of something coming into the Solar System. Something much bigger than cosmic rays or dust particles.

Asteroid/comet in hyperbolic trajectory

[Gerald]

The paper I mentioned above says at the end of page 1, that there is a discrepancy between the expected residence time of 2.5 Gyrs of a dust grain in the ISM and the expected lifetime of 0.5 Gyrs of a dust grain. Then they try to overcome this discrepancy by grain growth in cold molecular clouds (subsection 4.2):

The only possible site of grain growth in the ISM are the dense molecular clouds of the cold phase of the ISM (Draine 1990).

With the presence of interstellar comets and asteroids, I'm not sure, whether this conclusion is evident, since new grains could also form by collisions of small dust grains with these larger bodies, such that we should get a secondary population of interstellar dust grains made of debris, possibly statistically comoving with the (rogue) asteroids and comets. If this turns out to be realistic, we should get information about "interstellar interlopers" by the analysis of interstellar dust.
Since there may exist many such unbound small bodies, some useful result regarding an origin could only be obtained, if these small bodies form themselves a more or less comoving cloud, inducing such a co-motion into the according presumed debris made of interstellar dust.

[JRehling]

In our solar system, small (asteroid) and very small (dust) solid particles occupy a continuous distribution of size and occurrence, but there are many factors that hold constant in our solar system that will not hold for small bodies created galaxy-wide, and there are still more factors that will not hold constant for bodies that have crossed interstellar distances, and there is yet another striking selection effect in the fact that this thing survived a near-brush with the Sun.

The oldest stars in the universe would have no metals in them, just hydrogen and helium. There's no way to make a solid body out of those elements, so the source star has to be second generation, at least. But it might come from a system that has plentiful oxygen but nothing so heavy as iron or even silicon. Systems that are older will have fewer heavier elements, which would mean no rocks or even dust for the bodies in that system to begin accreting around. But it seems impossible for something made only of ice to survive that passage by the Sun, or even to be red. A younger system will have more of the elements to explain this thing's nature, but less time for the interstellar journey to have taken place. A lot of these factors are easy to mention in qualitative terms but are unconstrained quantitatively.

Other selection effects: Possibly the existence of giant planets that could have enabled a gravity assist to eject them this far, this fast. And that constrains the source star in ways that we don't yet understand. Juno and the newly-observed neutron star collision are both opportunities to learn the basics of how elemental/planet creation depends upon the stuff (nuclear chemistry) that's available.

So, there's a lot to learn about a lot. If anything, I think this discovery makes it seem worthwhile to prepare for future bodies, and if possible, to catch them and do in situ compositional analysis before they make any close approaches to the Sun.