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I'm looking for various factors; Atmosphere Composition, Type of Sun, etc, whatever would work. That is, of course, if this is even likely/possible. I believe that yellow is generally not an ideal color for foliage, save for attracting bees or something (Which may be myth, I'll have to research that). The environment in question should ideally be able to support human life (not necessarily related) but i can work with it if impossible. No need for paragraphs unless you want to.

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This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

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The reason plant leaves are green is because they contain the pigment Chlorophyll. Chlorophyll absorbs blue and red light while reflecting green light (thus making it appear green). The absorbed light energy is used for photosynthesis. The obvious way for a planet to have yellow foliage would be for the plants to use a different pigment for their photosynthesis that absorbs all except yellow light. I don't think you need to explain it beyond saying that the plants evolved differently.

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  • $\begingroup$ Although light on earth is predominantly blue because of the refracted sunlight in the sky, our sun is very yellow. The fictitious planet you're proposing should probably orbit a star that isn't as yellow as Sol. $\endgroup$ – BrettFromLA Apr 6 '15 at 20:33
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    $\begingroup$ @BrettFromLA Actually our sun is the very definition of white. But when you look at it directly the blue receptors in the eye fail first. Also when it is low refraction makes it appear yellow. The suns spectrum actually peaks in the green. $\endgroup$ – AstroDan Jun 28 '16 at 16:01
  • $\begingroup$ @BrettFromLA I just saw a bit grom Neil DeGrasse Tyson on that. If the sun were yellow, why is snow white?! Photographers know the difference in lighting color for direct sun vs shade: the direct light is more yellow because the blue is scattered and comes from all directions. Combined, you get white. But "white" is a calibration, and we automatically adjust for illumination. $\endgroup$ – JDługosz Jun 29 '16 at 21:08
  • $\begingroup$ Plants use chlorophyll because the Sun's peak wavelength is in the green range. They would overheat if they absorbed all of the energy. $\endgroup$ – undine_centimeter Dec 29 '16 at 22:01
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That's easy! On Earth, plants use two types of pigments to absorb light for photosynthesis. The most well known of these is chlorophyll, which absorbs blue and red light and thus appears green. But plants also use a class of pigments called carotenoids, which absorb green, blue and violet light and thus appear red, orange, or yellow. It is these pigments that are largely responsible for the color of fall leaves on Earth, as well as the color of carrots, egg yolk, daffodils, and canaries. A class of carotenoids called Xanthophylls are especially yellow compared to other carotenoids which may be more orange.

Carotenoids cannot operate completely on their own, and in Earth plants they must transfer their captured energy to chlorophyll, which then mobilizes electrons into the rest of the photosystem. One can imagine however a setup where the carotenoids transfer their captured solar energy into a molecule that replicates chlorophyll's ability to mobilize electrons but cannot absorb light by itself, or at least is sufficiently shielded by the carotenoids that its color (if any) doesn't show up.

Essentially, you want a photosystem where carotenoids are the primary light-gathering molecules and the separate electron-mobilizing molecules are either incapable of absorbing light themselves (which is more likely evolutionarily, else the carotenoids would not necessary) or tucked away inside dense packets of carotenoids (which makes sense from a structural point of view). As to what these electron-moving molecules could be, I don't know. Chlorophyll does this using a large aromatic ring with a central metal atom, but since these types of compounds strongly absorb light they might not be ideal.

So, what might lead plants to rely heavily on carotenoids and not on chlorophyll? The most obvious solution is to have a planet where the wavelengths of light available at the planet's surface are strongest in the range that carotenoids can absorb but chlorophyll can't. So the available light at the surface of your planet should be:

  • Very weak in the red portion of the spectrum.
  • Strong in the green portion of the spectrum.
  • Very strong in the violet portion of the spectrum.

Violet is your best bet for the strongest wavelengths because a plant that absorbs lots of violet light will appear more yellow. If we focused instead on the green part of the spectrum (where chlorophyll is weakest), the plant would look more red. The increased violet light might make your sky appear more indigo than Earth's pale blue, but atmospheric color is going to depend hugely on what gasses are present and in what concentrations.

Oxygen and nitrogen are pretty good at scattering violet light, but our sun doesn't emit enough of it for our sky to appear more violet. So you can probably achieve this effect simply by making the star emit a little more violet light. I'm treading on the limits of what I know here, but you can probably do this by either by changing it mass to be heavier or just changing its chemical composition (its spectral signature). If more violet light is being scattered by the atmosphere, the sun itself might appear a little more orange than it does on Earth. Regardless, sunlight would still be white light just like it is on Earth, and things on the surface wouldn't be colored differently.

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  • $\begingroup$ You might also need to distinguish what the leaf looks like in our lab with Earth lamps, vs what it looks like under that planet's daylight! $\endgroup$ – JDługosz Jun 29 '16 at 21:12
  • $\begingroup$ @JDługosz Any sun-like star is going to radiate so strongly across all visible wavelengths that its light will probably appear white disregarding any atmospheric effects. Our sun actually radiates most strongly in the green portion of the spectrum, but most ambient light is blue because of Rayleigh Scattering by oxygen and nitrogen. This is why I said "the wavelengths of light available at the planet's surface" and not "the wavelengths of light radiated by the planet's sun." $\endgroup$ – ApproachingDarknessFish Jun 29 '16 at 22:02
  • $\begingroup$ Yes, any black body radiation in a broad range of temperature will be adjusted by our eyes. But the light at the surface with strange filtering clouds or whatever is devised to give the needed spectum would look funny to us. $\endgroup$ – JDługosz Jun 30 '16 at 0:59
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  1. Find a yellow plant on earth. (Heuchera and gold Hosta are two examples.)
  2. Explain that evolutionarily, that was the earliest successful plant, and most/all other plants are a descendent of it.
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Your planet could be really low on iron.
There is a tree condition called chlorosis that is caused by low iron in the soil, and leads to light green/yellow leaves.

It could also be that the PH in the soil is to high, which keeps trees from absorbing the iron.

Or just go with Tom Andersons idea.

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    $\begingroup$ The link for chlorosis doesn't work, so here's an alternative link en.wikipedia.org/wiki/Chlorosis $\endgroup$ – god of llamas Jun 28 '16 at 12:36
  • $\begingroup$ @godofllamas thanks! The link has been updated. $\endgroup$ – AndyD273 Jun 28 '16 at 15:53

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