I have a world orbiting an M7 red dwarf with an atmospheric composition like this: 96% N2, 2% NH3, 1% Ar 0.5% CO2, 0.5% SO2+Others

At 0.2 bars, with an Ammonia ocean (if that changes anything)

What colour will the atmosphere be from orbit and from the ground?

I've gone online and seems that all the gases mentioned above are clear, does that mean the atmosphere would be clear?

  • $\begingroup$ What is the mass and luminosity of the star? While just knowing the spectral class is enough to have a vague range, it would be helpful to know the exact designation. Like, is it an M1, and M3, maybe M9? Just look on the wikipedia page and they have a list of spectral types for a Red Dwarf. If your specifications fall between two types, you can use decimals. I ask this as an M0 and M9 would bring about a very different sky colour. $\endgroup$ Oct 6, 2023 at 15:43
  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Oct 6, 2023 at 16:15
  • $\begingroup$ Do you mean the colour of the atmosphere from the inside, or from orbit? $\endgroup$
    – jdunlop
    Oct 6, 2023 at 18:54
  • $\begingroup$ You can not have ammonia in an atmosphere with oxygen because they will combine to form water (ice with your temperature) and nitric oxide, and you'll also get some nitrogen dioxide and nitric acid. Also be sure to add some argon to your atmosphere, as it forms from the radioactive decay of $^{40}K$, which is one of the main sources of natural radioactive decay in rocky planets. $\endgroup$
    – Neil Iyer
    Oct 7, 2023 at 0:09
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    $\begingroup$ @FoxStudios One thing, $SO_2$ (in your other 0.5%) and ammonia will combine to form red $HNSO_x$ polymers, so choose one to be in your atmosphere. That could be interesting though, having a $HNSO_x$ red polymer seafloor and ammonia oceans. $\endgroup$
    – Neil Iyer
    Oct 7, 2023 at 18:33

1 Answer 1


As the comments point out, this atmosphere is inherently unstable. There would need to be some biological or chemical process on the planet that breaks apart the rapidly-formed ammonium amide sulfate/ite.

But, since HNSOx is white, you can expect a light blue/cyan atmospheric color, assuming the star is similar to our Sun.


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