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A question somewhat related to this question.

Quick noble gases 101:

Helium is a light gas found in early primordial atmospheres, but quickly escapes into space and isn’t replenished by volcanism.

Neon is also a light gas that escapes easily (not as easily as Helium though). It vaporises easily and has no natural decay pathway for it to be replenished. It could only feasibly form in a terrestrial planet’s atmosphere if the planet were extremely cold.

Argon is ~1% of Earth’s atmosphere thanks to the decay of Potassium-40.

Xenon could accumulate in a terrestrial planet’s atmosphere if it formed from a supernova, giving it lots of radioactive isotopes like Uranium and Plutonium.

Radon has a half-life of 180 days. It won’t be able to accumulate.

Question:

What about Krypton? If I want this noble gas to form a non-trace amount (>1%) of an earth-like planet’s atmosphere, what planetary formation or decay pathway would be needed?

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  • $\begingroup$ Does anyone know if elements can get separated based on mass around black holes (particularly binary ones)? I imagine a planet/star system sitting in the LaGrange point of a binary black hole being bombarded by a stream of Krypton. It doesn't need to probable, only possible. $\endgroup$
    – DWKraus
    Commented Aug 6 at 14:35
  • $\begingroup$ The other scenario involves a fast-spinning planet having light gasses stripped off somehow based on mass. I'm not sure how to make the planet habitable afterwards, or move the krypton to another planet afterwards. $\endgroup$
    – DWKraus
    Commented Aug 6 at 14:41

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Krypton is also formed in the explosion of massive stars

Cosmological origin of each element of the periodic table

and I have found no naturally occurring decay chain which has Kr as an intermediate step.

I am afraid that the only natural way to have it accumulate in the atmosphere is for the planet to cross the expanding cloud of matter resulting from the explosion of a massive star and capture the Kr contained in it.

Or have a lot of nuclear incidents/test/explosions which release a lot of Kr isotopes.

I suspect that neither is going to be a fun experience.

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    $\begingroup$ What if a sufficiently powerful supernova went off nearby and the resulting cloud reached the system while it was still forming? $\endgroup$
    – JuimyTheHyena
    Commented Aug 6 at 15:54
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There are some, very theoretical, decay pathways to form more stable Krypton on an existing world, mainly by action of neutron radiation on Rubidium, or electron capture of Strontium (i.e. not under natural conditions you might expect to find on planet), and the percentages are low. Failing that your Krypton rich atmosphere has to start with a high abundance of Krypton produced by stellar action, period.

Furthermore because the unstable Krypton-81 is a cosmogenic nuclide derived from stable Krypton-80 by the action of cosmic rays the abundance of Krypton in the atmosphere is actually going to shrink over geological time, sorry.

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