Sooner or later every character eats some dust. Sometimes it’s stardust.
Apparently some scientists supported by, among other organizations, the French polar institute, have spent parts of the last twenty years, collecting dust in Antarctica. Interplanetary dust.
Their best estimates are that we get 5,200 tons of offworld dust a year, mostly from comets. Which implies that they may have even missed a few tons that came down as ice and sublimated. So whenever you go out in the rain, there’s a fair chance a tiny fraction of those chilly drops came by way of cometary express.
If, of course, the estimate is correct. If the scientists have correctly identified the heart of Antarctica as a place almost no terrestrial dust falls. If there’s no quirk of atmosphere, or how particles hit atmosphere, that might slant the numbers up or down.
Life has a lot of ifs in it.
Part of the fun of worldbuilding is you can grab specific ifs, say, “okay, I’m going to take this as a given,” and then extrapolate out from there what the consequences should be. For example, if we get water and dust from comets, and we sometimes get organic compounds that way, and we know the spores of some organisms can survive freezing and hard vacuum – then isn’t it possible that passing comets could deliver a microbial invasion?
In point of fact, people have long believed comets were bad omens, heralding death, invasions, and plague. Hmm.
Of course, following these ifs to possible conclusions can lead to you being up nights as effectively as any horror novel. After all, if the Antarctic science is right, we’re being “invaded” from space on a daily basis. And there’s absolutely nothing we can do about it. Suppose some species out there saw Earth and decided to put a quiet payload of death into the next passing comet. Why bother going to the risk and hassle of invading if you can just make sure the dominant sapient species dies out?
Ahem. People, we need to get our space program going. Not just to the Moon, or even Mars – we need to get all the way out to the Oort Cloud and beyond. Border control; it’s not just for nations anymore.
(That or think of it as defending our home ecology. Just in case.)
Remember, when you worldbuild: the ifs are out there.