Xenon-129
Xenon-129 is a stable isotope of Xenon. According to Good-ol'-Wikipedia's "Isotopes of Xenon" and "Xenon" pages, the natural abundance of xenon-129 on Earth is around 26.4% of all xenon, and the ratio of xenon-129 to 132 is just slightly less than 1. Oh, and xenon is a gas, and it comes from a long line of Nobility.
With that intro, now to the claim of it being on Mars. From what I could find, there is a December 1976 paper in the journal Science entitled, "The Atmosphere of Mars: Detection of Krypton and Xenon." The third sentence of the abstract states, "the ratio of xenon-129 to xenon-132 is enhanced on Mars relative to the terrestrial value for this ratio." It goes on to say, "Some possible implications of these findings are discussed."
To be completely honest, I was surprised. I did not expect this to pan out, given perhaps some of my more recent podcast episodes. So, what Viking found is that the ratio of 129 to 132 is not 0.97 as on Earth, but 2.5(+2)(-1) -- significantly more 129 than 132. But, that's as far as I can follow Brandenburg. For a couple reasons. Well, two.
First, I can't find anything about xenon-129 being produced in nuclear explosions. In supernovae, sure, those produce pretty much everything. They're an alchemist's dream. But not a nuclear weapon. The only stuff I could find on the production of xenon-129 is from the decay of radioactive iodine-129 into xenon-129. Iodine-129 has a half-life of about 16 million years, meaning that within 160 million years, less than 0.1% of the original amount of iodine-129 will remain. Meaning that all the iodine-129 originally part of any planet will have decayed by now into xenon-129 unless you're a young-Earth creationist. So, again, problem #1 so far is that unless this is top-secret knowledge or Google has failed me, xenon-129 is not produced in nuclear bombs. Which pretty much is the foundation of his idea.
It's possible he got fooled by the term, "radiogenic" xenon-129, and thought that meant nuclear reactor ... it just means that it's produced by radioactive decay of something else, in this case iodine-129.
It's also possible that his actual claim - even though I've never heard him state it - is that it's iodine-129 that is what's produced in a nuclear bomb, and since that decays into xenon-129, then that's evidence of the iodine-129 which is evidence for his nuclear war. Though I really don't want to make his argument for him, that is one possible way to save his idea. But, the 16 million year half-life of iodine-129 means that this would have had to have happened hundreds of millions of years ago for there to be no iodine-129 left and for it to all have decayed. Possible? I suppose, and I've heard stranger things.
But, the second reason I stop following Brandenburg's ideas at this point is for the same reason that Lawrence Livermore National Lab stated: There are a lot of possible geologic reasons why xenon-129 is more abundant relative to 132 on Mars than on Earth. The Science article points out that some types of stony meteorites have ratios of 4.5 or as high as 9.6, which is much higher than the Mars value, indicating that Mars may be sourced from more of that primitive material than Earth was as those slowly degassed into Mars' environment.
Another model by Musselwhite, Drake, and Swindle from 1990 suggests that the iodine originally incorporated into Mars was outgassed after formation into an atmosphere, but iodine was incorporated into the crust while xenon, being a noble gas, just stayed in the atmosphere. Then, lots of impacts happened in the first 500 million years, eroding Mars' atmosphere significantly including ALL the isotopes of xenon, mostly evenly. Meanwhile, the iodine-129 in the crust is decaying into xenon-129 and very slowly outgassed. As opposed to Earth, where it would be recycled and buried in the mantle due to plate tectonics. And, ¡voilà!, Mars' atmosphere is enriched with xenon-129. No nuclear holocaust needed, and this fits with everything else we know about how the planets work and it's supported by the ratio of argon-40 to krypton-40. The only small issue for this is the timing given the fairly short half-life of iodine-129.
Because of that timing issue, others have come up with other models for how Mars' atmosphere could be enriched in xenon-129. A popular model was proposed by Swindle and Jones in 1997 that proposes Mars started not with an asteroid-like composition, but an atmosphere like the solar wind. This allows a contribution from plutonium-244 -derived xenon-136 to be present which I guess somehow helps the models more accurately produce the xenon observed. And yes, I did say plutonium. Plutonium-244 is a very heavy isotope of plutonium, has a half-life of about 80 million years, and it's plutonium-240 used in nuclear weapons ... 244 is the most stable isotope of plutonium and still found in nature and it is not abundant in nuclear reactors though some is produced in nuclear explosions. So again, while this *could* be sorta used in a very round-about way to support his claims, it's hard to get there from what we know. Not impossible, but very hard.
At the very least, from this discussion of xenon-129, the conclusion that Brandenburg made - that it's only produced during big nuclear events, is not true. It's actually NOT produced in nuclear events - except supernovae - but it *can* be produced as a by-product of what is produced by nuclear weapons or reactors.
