# What levels of Argon and Neon (along with other factors) are needed to make the entire sky orange and sustainable for life?

I've read several sites and even questions on here where the sky would appear almost white or light blue if it orbited an orange dwarf star. However, that is if the planet has the same atmosphere as ours. But what if it didn't?

From what I read, different amounts of gases in the atmosphere might make the sky appear to be different.

Given these facts, what if the atmosphere of this planet was 75.09% nitrogen, 21.95% oxygen, 1.40% argon, 0.14% carbon dioxide, 0.29% neon, and small amounts of other gases.

For comparison, the levels of argon and neon in our atmosphere are 0.93% argon and 0.001818% neon.

However, this is just an example. My figures might be off and the levels are either too high or too low.

Also, there are probably other factors that are necessary for the sky to appear orange while the planet orbits an orange dwarf star.

My question boils down to this: what levels of Argon and Neon, along with any necessary other factors, are needed for this planet to have an orange/reddish-orange sky while orbiting an orange dwarf star and still be sustainable for life?

Sustainable for life I mean for anything that breathes oxygen! Or in this scenario, a species that evolves on the planet and breathes oxygen.

• For your perusal: worldbuilding.stackexchange.com/questions/100411/… – Arkenstein XII Jun 24 '19 at 0:12
• Well, that's for a normal Earth atmosphere with the same composition as our own. I think. I mean could more argon and neon change the color of the sky? – SCPilot Jun 24 '19 at 1:01
• Well, does give me some ideas for other alien worlds. So thank you! – SCPilot Jun 24 '19 at 1:06
• The value of that chart is if you can determine what the color of Earth's atmosphere would be given the addition of Argon and Neon could be determined, that chart would tell you how to shift the color due to the star color. It saves you a step during the analysis. Now comes the hard part... what does Argon & Neon do? Can you be more specific about the % you're looking for? "A bit more" is awfully vague, considering how small the quantities are right now. "A bit more" wouldn't do anything. – JBH Jun 24 '19 at 1:21
• Both argon and neon are are colorless gases. The orange neon glow happens when the gas is excited by an electric discharge. – AlexP Jun 24 '19 at 1:55

1. Human vision is very sophisticated at filtering out colored illumination – basically, whether the sun is very red or very blue, our eyes and brains define the color of sunlight to be "white" and shift our perception of other colors accordingly. Even under sodium street lamps, we see trees as green and so on, despite the fact that a photo will show that everything in the scene has the exact same yellow hue. (This phenomenon is what "white balance" in photography corrects for).
The significance of this is that, for the sky to appear orange, it must be orange-hued relative to the source of light. Which means that you would not get an orange sky by making the sun orange (either by lowering the star's emission temperature or by adding an orange "filter" in the atmosphere).

2. For the sky to reflect orange light, it would need reflective particles, which would mostly just reduce the amount of light. That is, if you try to make the air look orange by spraying orange paint around, the light will get dimmer much faster than it changes in hue.

3. The scattering that makes our sky blue can also make it orange, depending where you're standing. The sun is constantly firing bullets of light in all directions, and the bluer bullets are more likely to ricochet off an air molecule along the way (without affecting the overall amount of energy / illumination).
So, if you're looking at the sky with the sun off to one side, the bullets from the sun don't hit your eyes directly, but you do see the bullets that get scattered as they're flying over your head – you see the scattered blue light, which is why the sky looks blue.
But if you are facing toward the sun, the sky in that area looks more orange because a greater proportion of the blue bullets have been deflected before they hit you, so it's the redder light that is left over. For various reasons, we don't tend to notice this at midday, but it is very noticeable in sunsets, where you do indeed get orange skies.
The physics of this aren't really negotiable – scattering makes light redder from the front and bluer from the side, period. But you could certainly contrive a way to have a sunset that lasts all day.

4. If the sky is otherwise dark – because the sun is dim, or at night – then you can have gases in the atmosphere emit light by corona discharge, i.e. an aurora. The color is determined by the gases involved, and the intensity is determined by the strength of the ionizing radiation hitting the atmosphere. However, the physics determining light color are quite complicated – Earth auroras are mostly green and red, with both colors being due to atomic oxygen (O•) at different altitudes. High concentrations of neon probably would give you red auroras, but the problem is that neon, like helium, is so light that it would boil off into space. Another problem is that if you want auroras over the whole planet, it implies there is a lot of cosmic radiation and no magnetic field, which makes it questionable whether you would even have an atmosphere or be able to support life.
If you wave away that concern, you could have a red aurora covering the entire sky, produced solely by atomic oxygen at high altitude. In order to get rid of the green light, you could say that the atmosphere has no nitrogen at all (since molecular nitrogen is required for the process whereby oxygen emits green light). You could replace the nitrogen with more oxygen, though you'd have a very flammable planet, and humans can't breathe such a rich mix at Earth-normal pressure. Or, you could replace the nitrogen with argon, except I think that would anaesthetize humans at high concentrations. Or you could just assume that there is a workable mixture somewhere between the two.

Color of a sky is due to Rayleigh scattering. It means it doesn't depend much on atmosphere composition (only small tints). Yes, even on Mars sky is blue, unless for dust storm. And thats how you can "paint" your atmosphere - use some aerosol. Say planet is covered with dence mono-species forest wich constnatly emmits lots of orange pollen or smth like that.