Another Interstellar Asteroid - This One a Permanent Resident of the Solar System

Asteroid BZ interested astronomers right away, because it is retrograde, in a 1:-1 resonance with Jupiter - suggesting that it was captured from outside the solar system just as ours formed, and is therefore older than the rest of the solar system.

But more interesting than that, it took several unlikely events for it to be captured and continue in a stable resonance over time (see last paragraph in the Orbit section.) This very strongly suggests that there are interstellar objects passing through the solar system all the time. For such an object to be captured so quickly, so early in the history of the solar system means that there must be enough of them to get trapped by freak aligments. Another way of looking at it is that fast = likely.

This is consistent with a similar argument made about Oamuamua, an interstellar asteroid that is currently passing rapidly through the solar system. Within a year of the first telescope that could detect such an object being activated, it found such an object. Good luck? Or constant interstellar material passing through? (It didn't take long to find BZ either, once we started looking.) The relevant point is that while the vast distance between stars is often cited as a form of quarantine for macroscale beings like us, it is certainly not such a quarantine, even on brief geological time scales, between pools of organic molecules. More here about periodic close passes between stars and interstellar mixing here and here, and (most speculatively) that if von Neumann probes exist, they are likely to interact with comets and asteroids with organics, rather than planets.