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First Extrasolar Object Observed Racing Through Our Solar System (space.com)
Enigma2175 writes: For the first time, scientists have observed an object they believe came from outside our solar system. The object is in a hyperbolic orbit that will send it back into interstellar space. From Space.com: "The object, known as A/2017 U1, was detected last week by researchers using the Pan-STARRS 1 telescope in Hawaii. 'It's long been theorized that such objects exist -- asteroids or comets moving around between the stars and occasionally passing through our solar system -- but this is the first such detection,' Chodas added. 'So far, everything indicates this is likely an interstellar object, but more data would help to confirm it.' It's unclear what exactly this thing is. When A/2017 U1 was first spotted, it was thought to be a comet (and was therefore given the moniker C/2017 U1). But further observations have revealed no evidence of a coma -- the fuzzy cloud of gas and dust surrounding a comet's core -- so the object's name was amended to its current asteroidal designation."
>We know the chances of being hit by an object by looking at how many objects hit planets.
Also, to some degree, by common sense. Most of the dust spinning around our star that is going to collide with something has had five billion years to do so, and the clumps of matter formed in the process do a fairly good job of sweeping up the leftovers around the edges before they can get as close to the Sun as we are here on Earth.
I am not an astronomer, but I would anticipate that (given our star formed later than most) most of our neighbouring systems are in a similar state or even more orderly, so they wouldn't have much left in the way of significant rocks to lose to us in any gravitational tug-of-war.
And after that comes the fact that space is huge relative to the Solar System (making it unlikely any rogue rocks will come significantly within its gravity well), and the Solar System is huge relative to the Earth (making it unlikely any rogue rocks that actually venture into the Solar gravity well will also dip into Earth's). And the Earth itself is tiny so even something flying through our gravity well isn't particularly likely to impact our planet if it's travelling faster than Solar escape velocity (which it pretty much has to have been after falling into the Solar gravity well from outside it).
I gotta tell you... I am not particularly worried about my lack of insurance coverage in the event of loss due to extra-Solar impactor.
In this case, the margin I have in mind is in kinetic energy terms. It won't end up infinitely far away because it is nowhere near galactic escape velocity.