So in this world I was writing about I need one exclusive zone of the planet to be purple and their plants to be adapted to this atmosphere.
What would I need?
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$\begingroup$ Any high layer that absorbs green, but lets red and blue through. Volcanic dust, plant spores, whatever. $\endgroup$– user79911Commented Nov 8, 2020 at 11:09
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$\begingroup$ Please note that plant color has nothing to do with atmospheric color and only a little bit to do with star color. Also, consider the answers to "I'm trying to create a planet with a purple sky...." $\endgroup$– JBHCommented Nov 9, 2020 at 0:20
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3 Answers
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To get a purple sky you need either:
- A thin band of iodine gas very high up, and very hot.
- Polarised light, so have the light pass through a (hadwaved) filter which filters it.
- Triflouromethyl nitrite in the atmosphere.
- An intermediate gas gloud between the planet and the sun made of something which is transparent to all but green wavelengths. Perhaps a very thin green-absorbing algea shell high in the atmosphere
- Any process emitting red and blue light. Eg two vastly different suns.
What do plants look like that must survive on purple light?
Exactly the same as normal plants
Purple lights are used by indoor plant growing setups all the time, the one I linked to there is advertised at 70% efficiency gain over white light for the same amount of final crop.
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$\begingroup$ Bullet #1 works, but creates a toxic atmosphere (no way to keep it high enough up, it's heavier than oxygen). Bullets #2-4 don't work because Rayleigh scattering always scatters in the blue spectrum. Note that star color has nothing to do with atmospheric color (Rayleigh scattering...). $\endgroup$– JBHCommented Nov 9, 2020 at 0:25
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Purple haze.
This region has airborne bacteria in such quantities that the light filtering thru them is purple.
Start with autotrophic bacteria which are purple from their photosynthetic pigments. Here are some good ones!
https://www.yukon-news.com/news/the-purple-bacteria-of-two-horsemen-lake/
These purple organisms generate intracellular hydrogen, as I proposed in this idea: Which conditions would make aerial filter feeding successful?
They hydrogen makes them neutrally buoyant. High relative humidity keeps them from dessicating and they can fix their own nitrogen. They live in the air all the way up to where atmospheric pressure is so low they dry out.
Beneath the purple haze, it is dim and ... purple. Also, dead organisms fall from the sky periodically. They are still purple when dead, and so things on the land beneath gradually become purple as well.
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Frame challenge. It's all in the eye of the beholder.
You are on an alien planet. Therefore I assume you have aliens with ... alien physiology.
Light works the same way but your aliens eyes are designed to view a different wavelength of the light spectrum. So their world looks purple to them, while to us regular humans their world looks more blue, or green, or dusty red.
answered Nov 8, 2020 at 23:43
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$\begingroup$ Ah you see though, colors are relative. There is now any to guarantee that the way you see purple is the same way as I do. Therefore if the aliens interpret blue to be purple, that is the same thing as telling me that the color blue is in reality purple. Therefore your logic is inconsistent... I will revert my downvote if you could explain yourself more thoroughly... $\endgroup$– fartgeekCommented Nov 9, 2020 at 0:07
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$\begingroup$ This reflects an answer over on Physics.se. It remarks the fact that humans don't see in the violet spectrum well, which is why we tend to see blues. Consider the article Earth's Skies are Violet - We Just See Them As Blue. $\endgroup$– JBHCommented Nov 9, 2020 at 0:27
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$\begingroup$ @fartgeek. It's not so much that the same wavelength is being interpretated as different colours (which is basically opinion) but rather that two different wavelengths are being viewed and are therefore being interpetated as different colours. The aliens are not viewing what we call blue, as purple. Rather the aliens are viewing wavelengths we can't see, such as what we call ultra-violet. If they decide to call it purple or blue...that's on them. $\endgroup$ Commented Nov 9, 2020 at 1:15
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$\begingroup$ Hmmm fair point, not completely satisfying but good enough for me... if you would edit your post so I can change my downvote... $\endgroup$– fartgeekCommented Nov 9, 2020 at 1:49