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This question already has an answer here:

For my current Eclipse Phase campaign/Fan Fiction I set up a "habitable" Gas Giant, by habitable I mean, that there is a layer in its atmosphere, where 1 bar of pressure and a temperature of ca. 283 K more or less coincide.

(What can I say, I love my cloud cities.)

The surface would, of course, still a metallic hydrogen ocean and a very unhealthy place to be.

  1. Is there anything that would rule out this set up? Anyone would like to take an educated guess at the atmospheric composition or distance from its star? One assumes that a "hot jupiter" would be more likely for this?

  2. I provisionally named the place Lapis-Lazuli and have a lot of fluff written out, going on about its aquamarine/ultramarine cloudscapes, fading to jade. I'm kind of fond of it and would like to keep if, but the methane ice, which give the blue coloration has a melting point of 90 K. Would the gas also work? If not, is there some other kind of chemical composite, which would have the same visual effect?

    2.1 To clarify, when I say aquamarine cloudscapes, I would like to have a blue sky from the Rayleigh-scattering (Is there any reason that should be different for an atmosphere of, say, primarily Hydrogen, Helium, Methane and Water Vapor?) and the cloud decks itself.

  3. Is there any particular reason, why a gas giant could not have a noticeable partial oxygen pressure?

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marked as duplicate by Mołot, TrEs-2b, Hohmannfan, John Dallman, Magic-Mouse Oct 5 '16 at 12:42

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    $\begingroup$ Hi, I'm currently working on an answer for your question. However for a easier choice of colours it would help to have visual confirmation of colours, that also have a given spectrum. I found the site minerals.gps.caltech.edu/FILES/Visible/Beryl/Index.html maybe you can point me in the direction of the colours there? The spectrum of a colour plays a role, as I'm gonna try to derive a possible matching composition of your gas giant atmosphere for the given spectrum. $\endgroup$ – AtmosphericPrisonEscape Oct 4 '16 at 21:01
  • $\begingroup$ @Molot: The answer in the question you highlighted is heavily outdated and does not adress the question of colour, which involves quite some calculations. $\endgroup$ – AtmosphericPrisonEscape Oct 4 '16 at 22:14
  • $\begingroup$ @AtmosphericPrisonEscape that's awfully nice of you, thanks. Let's try with the GRR 1716 spectrum? If you have time and inclination, maybe you could also have a run at the GRR 3040 spectrum and GRR 1488 spectrum? I don't want to consume too much of your time on a fan fiction project. $\endgroup$ – HobbsTunaSandwich Oct 5 '16 at 8:06
  • $\begingroup$ @HobbsTunaSandwich: No worries, i'm doing it to learn more about how efficiently different molecules scatter light. Until now I have some chemical profiles for a warm-Jupiter like atmosphere with the specifications you need. What remains is to write a little scattering code for those atmospheres and see what spectrum looks best. Could take some days though until I can come back and finish that, a little busy right now. $\endgroup$ – AtmosphericPrisonEscape Oct 5 '16 at 9:37
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There is indeed a reason why a gas giant with an atmosphere containing hydrogen, methane or other gasses that burn in oxygen in significant quantities cannot also have significant quantities of free oxygen in its atmosphere.

Lightning.

It happens in many kinds of atmosphere, and has been observed on Jupiter. It will ignite any flammable mixture. Earth's atmosphere contains lots of oxygen, because most things that will oxidise have already done so. The levels of methane and hydrogen in the atmosphere are tiny, far too low to sustain combustion.

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  • $\begingroup$ So there's an abundant source of natural electricity. What's the problem? :) $\endgroup$ – Frostfyre Oct 4 '16 at 19:39
  • $\begingroup$ Ack! Planet wide Firestorms take the fun out of anything. Good point. <br><br>Quick Edit: Wikipedia seems to indicate the Limiting oxygen concentration, below which combustion will not occure, for Hydrogen is around 5 % for Methane around 15. So an Oxygen content of 4 to 5 % should be fine, right? $\endgroup$ – HobbsTunaSandwich Oct 5 '16 at 7:48
  • $\begingroup$ @HobbsTunaSandwich: Don't worry, typical gas giant atmospheres don't have that much oxygen or methane. We should be able to find a composition that doesn't ignite, but is still blue-greenish. For breathing purposes however, I'd still suggest your people should wear oxygen-masks, even if pressure and temperature are fine. $\endgroup$ – AtmosphericPrisonEscape Oct 5 '16 at 9:36

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