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I'm creating a world with three-quarters the gravity of Earth, and the composition of the atmosphere is as followed:

  • 74% Neon (or Argon)
  • 18% Nitrogen
  • 5% Oxygen
  • 1.6% Carbon Dioxide
  • 0.9% Water Vapor
  • 0.5% Trace

The questions I have in mind are:

  • Would Neon or Argon work better for this planet?

  • Could the atmosphere exist with the low gravity?

  • Could life as we know survive on this world, and could organisms evolve in a way to biologically contain neon/argon to use as bioluminescence?

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  • $\begingroup$ argon is heavy 74% is a catastrophic level of greenhouse gas... your planet would be a desert ball of fire, on earth 0,04% of greenhouse gases on the atmosphere are just enough to put the world at great risk, and our greenhouse gases are way lighter than argon. $\endgroup$
    – Charon
    Aug 15, 2016 at 19:18
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    $\begingroup$ @渡し守シャロン Argon isn't a greenhouse gas; heat goes through the certain wavelengths that trap heat. Are you saying because the atmosphere would be so dense that it would reek havoc on the planet's surface? $\endgroup$
    – Twig
    Aug 15, 2016 at 22:42
  • $\begingroup$ I'm not sure this can work, for reasons mentioned in the accepted answer to your other question. Life on Earth relies on the nitrogen cycle, which is itself based on Earth's atmosphere being three-quarters nitrogen and how that nitrogen reacts chemically with life. If you replace most of that nitrogen with one of the noble gases like argon or neon (known for their lack of reactivity), I'm not sure you can have any life, at least not anything we'd recognize. $\endgroup$
    – Palarran
    Aug 15, 2016 at 23:20
  • $\begingroup$ @Palarran the life on the planet might evolve to use the nitrogen more efficiently. In any case, "atmospheric life" is relatively new, most of the time the life evolved in water, so it is the concentration of nitrogen in water which matters. $\endgroup$
    – user31264
    Aug 16, 2016 at 0:00
  • $\begingroup$ @Palarran How much of the atmosphere should be nitrogen in order to sustain life; would it have to be the main component of the atmosphere? $\endgroup$
    – Twig
    Aug 16, 2016 at 0:29

2 Answers 2

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If it has a powerful magnetic field, 3/4th G should be more than enough to hold onto an atmosphere. A magnetic field has a lot more to do with keeping an atmosphere than raw gravity, because it keeps it from being stripped away by solar wind. Look at mars, for an example - Its magnetic field died long ago, and the sun slowly eroded the atmosphere away, but its gravity is only a third of earths. Titan, on the other hand, has only 1/6th earth gravity, but has a healthy atmosphere because it's protected by Saturns magnetic field. Also, argon, being heavier, would make for a denser atmosphere, so you could achieve earth-like pressures even with the lower gravity (if you want to.)

As for the composition itself, neon and argon are just as inert as our nitrogen, so whatever life there is is probably going to be oxygen-breathing. Oxygen is the most reactive element in the universe, so it only makes sense to use it in your biochemistry. That being said, if they were to visit earth they'd probably suffer oxygen toxicity, since they're used to breathing a very rarefied mixture.

As for the lights, sure, why not? It might actually be easier for them to develop the technology - Gas discharge lamps simply excite Argon/Neon/Xenon/Ect until it starts to glow. We have to contain the gas in a bulb because if we don't it'll diffuse into our nitrogen (and non-Argon/Neon) atmosphere. On the world you're talking about, something as simple as a static spark would have an orange or violet glow. I'd imagine them having some very pretty thunderstorms.

Side benefit: Any kind of Taser or Laser weapon that has a mundane invisible beam on earth would be very vibrant and colorful on their world.

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  • $\begingroup$ Titan orbits Saturn not Jupiter lol, and Titan can sometimes face the brunt of the solar wind since it is not always fully protected. The gravity of Mars isn't 1/2 it is about one third at 0.37 G $\endgroup$
    – Stephanie
    Aug 15, 2016 at 20:44
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    $\begingroup$ @Stephanie I always derp out and confuse jovian and saturnian moons. It's a personal weakness. $\endgroup$
    – UIDAlexD
    Aug 16, 2016 at 0:12
  • $\begingroup$ @Stephanie - maybe this will help you sort out that confusion. I've found it really helpful for visualising all the smaller bodies in the solar system. planetary.s3.amazonaws.com/assets/images/comparisons/… $\endgroup$
    – Simba
    Aug 17, 2016 at 8:32
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    $\begingroup$ Oxygen is far from the most reactive element. Fluorine is much worse. $\endgroup$
    – Logan R. Kearsley
    Sep 3 at 15:42
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One problem with reality check: if such atmosphere is possible that would require clearly different planet creation. Earth was stripped of its atmosphere at least during Late Heavy Bombardment. (or more timess) All atmosphere was lost, and a new one was formed. That's why we have only trace amount of neon in our athmosphere, even though it's abundant in the universe. We have argon, only because it used to be radioactive potassium which underwent beta decay.

(My only idea is forming this planet in some slow accretion way far away from its parent star, and let it later migrate. But it would create a melted ice world, which would have only sea surface)

If you have such quantities of argon (which is more plausible) than your planet used to be really radioactive...

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