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You've answered your question in your first paragraph - anything travelling faster than 72km/hr has come from outside our solar system. I learned, while watching a video on just this subject, that there was an estimate that 15% of meteors have an interstellar origin, detectable by their faster-than-solar-system-escape-velocity speeds. I had just assumed that all meteors were of our solar system origin until I watched this. Now it seems obvious - after all, where to all those comets go that get thrown out by passing too close to the sun, like comet McNaught? And recently there was speculation that a comet from another solar system had been detected (its chemical make-up was quite different to what most comets are). So there is some exchange over stellar distances.
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