# Sources of Xenon or other noble gases in space?

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.

Xenon can be found elsewhere. Wikipedia's Xenon; occurrence and production mentions a relatively high abundance of xenon on Jupiter, which is actually unexplained. But xenon is overall among the rarest elements everywhere, because of its high atomic number (requiring special processes to synthesize) and it's low tendency to form compounds.

Within the Solar System, the nucleon fraction of xenon is $$1.56 \cdot 10^{−8}$$, for an abundance of approximately one part in 630 thousand of the total mass. Xenon is relatively rare in the Sun's atmosphere, on Earth, and in asteroids and comets. The abundance of xenon in the atmosphere of planet Jupiter is unusually high, about 2.6 times that of the Sun. This abundance remains unexplained, but may have been caused by an early and rapid buildup of planetesimals—small, subplanetary bodies—before the heating of the presolar disk. (Otherwise, xenon would not have been trapped in the planetesimal ices.) The problem of the low terrestrial xenon may be explained by covalent bonding of xenon to oxygen within quartz, reducing the outgassing of xenon into the atmosphere.

Two (chemically) inert fission byproducts of Uranium 233 are Xenon 135 and Krypton 85. Though unproven and purely speculative, it might be feasible to power a spacecraft's electrical needs with a uranium powered fission reactor that can reject those elements and use them as reaction mass for electric propulsion.

It should be noted that both of these fission byproducts comprise a small percentage of the nuclear fuel's mass so they'd be useful only as a supplement rather than primary source of reaction mass. Additionally, Xe-135 has a very short half life of 9.5hrs, so it's a "use it or lose it" fuel.

Lastly, the hardware required to extract and prepare these elements for use as a reaction mass might only make sense in large scale spacecraft.

• I think the question asks for "...sources of xenon in space outside of planetary atmospheres." I suppose BYOB could technically qualify as a source in space, but at that point, why not just bring some xenon in a little bottle instead of collection fission products from your own nuclear waste? – uhoh Mar 5 '19 at 6:34
• Interesting. Xenon 135 has a short half life but Xenon 136 has a very long half life. As a neutron absorber Xe135 slows nuclear reactions (poison is I think the word commonly used), so it might not be ideal. Xenon 135 may have played a role in the Chernobyl accident as well, at least, I read that but I'm getting off topic. I had no idea nuclear energy was so complicated. – userLTK Mar 6 '19 at 7:42
• @userLTK, Xe-135 is indeed a very strong neutron poison which is why it needs to be removed from the reactor anyways. In solid fuel reactors, it also has the nasty habit of forming gas bubbles and cracks in the fuel rods. Those cracks weaken the overall structural integrity of the fuel rod, causing them to need to be pulled from the reactor prematurely. – Justin Braun Mar 6 '19 at 22:59