[X] My Assistant

[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]

A coating of a few microns of a pigment like tholins should provide the visible color of the object. The interior may well be rocky. The color of tholins will also win over the colors of translucent minerals like silicates in a mineral-tholin mix.
A considerable portion of the material of a stellar system is probably ejected during the first few millions of years after its Jeans collapse,
A rocky body of the inner stellar system may travel through outer parts or interstellar dust clouds, and collect a coating of tholins.
Tholins should survive for some time in an inner stellar system, before they will be degraded by stellar wind or micrometeorites.
That's just one out-of-the-hip scenario. There are certainly many more of varying likelihood.

Amalthea seems to be dark red. It's not in the inner solar system. But it's an example of a small red body with the potential to be ejected by close encounters or collisions. The composition of the interior of a small body depends mostly on its origin. An outer layer may have accreted later, in a new environment.

[JRehling]

A/2017 U1 had no observed coma, so it had little in the way of volatiles, at least near the surface. It could have had volatiles below a darker "crust" that didn't break through, but a dark object passing 0.2 AU from the Sun should have heated up quite a bit. It might be a chip off some exosystem's version of Mars. The surface color might be a thin coating or go all the way down. It's certainly spent a lot of time in interstellar space, which may have caused slow but thorough transformations that nobody's yet imagined.

I'd guess that in future decades we'll be able to spot much smaller versions of this thing which visit the solar system with considerable frequency and we'll start to explore them. There's a lot of untapped potential for huge light-bucket telescopes to monitor the skies and then things that are dimmer and dimmer will be detected earlier. If the size distribution of interstellar objects is like that of the asteroids in our solar system, then at some size threshold, there seemingly must be interstellar interlopers every year. But the process of interstellar travel might introduce some unimagined selection effects. For one, reaching the escape velocity of a star may be extremely violent.