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In my story scientists discovered a planet that look green from the telescope and they used a advanced starship to go there and the y found out that the planet is habitable with a breathable atmosphere but it has an exotic feature: The sky of the planet is green.

I know that the sky is blue die to Rayleigh Scattering which means that the small molecules that makeup the atmosphere like the oxygen and nitrogen reflect and scatter the blue light which has a short wavelenght but what about some other molecule in the atmoshere that would make the sky look green? This molecule would need to be harmless and be bigger than the oxygen and nitrogen ones since bigger molecules are able to reflect bigger wavelenghts of the visible spectrum(green has a longer wavelenght than blue) and would also makeup a substantial percentage of the planet's atmosphere.

What kind of molecule could it be? And what kind of atmospheric charactristics this planets should have in order to have a green sky(pressure, thickness etc)?

JBH
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Sabrine Crystal
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  • Don't forget that you can get some help here by changing the color of the planet's star. Stars can shine red, orange, yellow, white, blue, and all colors in between. You can't simply make the sunlight green, but you can change the base color mix that enters the atmosphere so that your atmosphere has a smaller/easier job shifting it to green. – Tom Mar 13 '22 at 20:41
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    A long time ago I read a paper that demonstrated that Rayleigh scattering of any and all gases would scatter in the blue spectrum (regardless the star color). Making an atmosphere look green in the same way that our atmosphere looks blue is, regrettably, impossible. The idea of scattering cell-sized green something (plants, minerals... you'd have a better chance with green crystalline dust) would help, but putting enough into the atmosphere to make it look green and not blue but still be habitable is a stretch. Oh, and you're mis-using the [tag:reality-check] tag, so I removed it. – JBH Mar 14 '22 at 07:15
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    If Rayleigh Scattering can only make the atmosphere look blue no matter tge composition so how is possible for Mars atmosphere to be yellow/brown? Venus atmosphere is also yellowish. – Sabrine Crystal Mar 14 '22 at 19:02
  • Closely related question: is there any way to make an earthlike planet (aside from the atmosphere) have a green sky at noon and a pink sky at dusk – Starfish Prime Mar 16 '22 at 12:56

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I believe that the new discovered planet would not even need a molecule that reflect green light but its atmosphere could be rich in aeroplankton which would have clorophill in order to carry out photosynthesis and therefore this planet's sky would look green considering that my fictional planets orbits a G Main sequence Star like the Sun.

Sabrine Crystal
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  • How much aeroplankton? – Daron Mar 13 '22 at 16:35
  • I believe that 100 - 300 grams of aeroplankton per cubic metre of air could be enough. – Sabrine Crystal Mar 13 '22 at 16:53
  • That sounds like a lot compared to the weight of the air itself. How does it stay up there and not fall down? – Daron Mar 13 '22 at 16:57
  • The aeroplankton themselves would be small enough(cell sized) to float in the air and be carried by the wind. – Sabrine Crystal Mar 13 '22 at 17:30
  • The air can only hold so much stuff -- however small -- before the stuff falls down. It is like the dust in your house. You might see some suspended in a light beam. But eventually it will fall out of the air and you end up with dusty surfaces. – Daron Mar 13 '22 at 17:57
  • Let's say a bathroom is about 6 cubic metres. Imagine you sprayed 600 grams of dust into the air. How long do you think it would stay up there? – Daron Mar 13 '22 at 17:59
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    Air pollution is measured in micrograms per meter cubed (mistyped before) , a bad smog would be between 200-500 micrograms per meters cubed. – UVphoton Mar 13 '22 at 23:08
  • Aeroplankton seem to be pretty small, only a couple of microns in diameter, they could stay suspended I. The air possibly a long time like 2.5 um carbon particles that is the size that EPA cares about since below that size they can get stuck in the lungs. – UVphoton Mar 13 '22 at 23:12