Xenon is a common choice for ion thrusters, though other heavy noble gases could work due to their low ionization potentials.
I got thinking about building or refilling future space travel ion engines with Xenon (or other if it's easier) and I wondered if the Xenon would need to be supplied from Earth.
Nobel gases are common enough in the galaxy but rare on planets or moons that don't have atmospheres. Earth has about 50 parts per billion in Xenon in it's atmosphere and Mars, 80 parts per billion in it's thin atmosphere. Both, in total are enough to supply thousands (in the case of Mars) or millions (Earth) of ion engine refills, so it's not a shortage, it's just a question of whether the cost of launching Xenon canisters from Earth is likely to remain cost effective.
So, my question is, are there a good sources of Xenon in space outside of planetary atmospheres. My guess is that there aren't and any ion flights, not just in the near future but over the next century or so, Xenon for ion engines will be launched from Earth.