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)?