Using the following list of stars, what color is the most efficient for plants to absorb the ideal amount of energy? (This is not a complete list of star types, just some big examples)

  1. Yellow Dwarf Stars
  2. Orange Dwarf Stars
  3. Red Dwarf Stars
  4. Brown Dwarfs
  5. Blue Giant Stars
  6. Red Giant Stars
  7. Red Super giant Stars
  8. White Dwarfs

Note that the plants on earth are green to reflect that part of the spectrum of light, even though it would be very efficient for plants to use that light. This is probably because using green light is too energy intense for plants to not be damaged. (Based on my understanding and this article https://www.researchgate.net/post/Why_are_plants_green)

So it would follow that other stars of different types may not produce plants of the color most efficient, but of a safe color for the plants ,and high enough in energy to support them.

So where do we begin? The color of the light produced by stars? For example, our sun is a yellow dwarf, and it produces all colors of the spectrum, but green is the most intense, and the plants on earth are a majority green. So do these hypothetical plant colors match the most intense color of light coming from their sun to protect themselves from it? Or as this article says, it may be as simple as the color the plants receive the least of.

"Scientists have long known that the chlorophyll in most plants on Earth absorbs blue and red light and less green light. Therefore, chlorophyll appears green. Although some green color is absorbed, it is less than the other colors. Previously, scientists thought plants are not efficient as they could be, because they do not use more green light. According to scientists, the Sun has a specific distribution of colors of light, emitting more of some colors than others. Gases in Earth's air also filter sunlight, absorbing different colors. As a result, more red light particles reach Earth's surface than blue or green light particles, so plants use red light for photosynthesis. There is plenty of light for land plants, so they do not need to use extra green light. But not all stars have the same distribution of light colors as our Sun. Study scientists say they now realize that photosynthesis on extrasolar planets will not necessarily look the same as on Earth" -https://www.nasa.gov/centers/goddard/news/topstory/2007/spectrum_plants.html

My second, and more specific question is, what color of star would encourage a blue color scheme in plants? I am working on an earth-like planet and am looking for a way for the vegetation to be blue-based. Is it as simple as picking a blue star, or are there some subtle nuances I am missing out on, like the article previously mentioned stated?

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    $\begingroup$ The question is based on a faulty assumption. There is no relationship between the power spectrum of solar light available on the surface and the greenness of Earth's plants. It is an accident. It so happened that the ancestors of land plants were among the green algae. It could as easily have been that the land plants developed from brown algae (Phaeophytes), or red algae (Rhodophytes)... $\endgroup$ – AlexP Nov 25 '19 at 22:49
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    $\begingroup$ Just as important as the light that's emitted by the star is the light that's absorbed by the atmosphere $\endgroup$ – Punintended Nov 25 '19 at 22:51
  • $\begingroup$ Is the difference between the spectra of different star types really that significant? Or significant enough to something making use of the more abundant color would be able to outperform those utilizing a less abundant color? $\endgroup$ – Michael Richardson Nov 25 '19 at 23:10
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    $\begingroup$ ebscohost.com/uploads/imported/thisTopic-dbTopic-1033.pdf $\endgroup$ – Snowshard Nov 26 '19 at 1:21
  • $\begingroup$ The document @Snowshard links to is very interesting. OP, it's a Scientific American article about exactly this topic, and I strongly recommend it to you $\endgroup$ – Astrid_Redfern Feb 20 '20 at 7:51

Let's clear up a common misconception before we get into the meat of the answer; the colour of a star is more to do with its energy output, although it can be affected by the Doppler Effect as well (stars moving away from us will appear redder, stars coming closer will appear bluer) if the relative velocities are high enough. So, no; it's not as simple as picking a blue star to get blue plants.

In point of fact, we can open our game up immensely - visible light only represents about 0.0035% of the Electro-Magnetic Radiation (EMR) spectrum, so on some exoplanets it's entirely possible to have plants with an X-Ray or Microwave colour - we just couldn't see that colour with the naked eye. To us they would probably just appear black. On the other hand, a plant that ONLY absorbed microwave radiation (for example) may actually appear white to us.

Why would evolution design an eye that can only see such a small amount of the EMR spectrum? Well, for one thing it's more than enough to cope with our sensory needs, so no need to complicate things, but for another if we could see ALL EMR, then we would barely notice a difference between day and night because we would be constantly bombarded by the 'light' from the stars.

So, on a rogue planet, where light only comes from distant stars, or even on a planet as far out as (say) Neptune is from our sun, it's possible that plants would develop colours we have no frame of reference for because they would absorb all the radiation they can get their hands on.

This of course brings us to the important part of this answer; it's not so much the energy output of the star that counts. It's the other factors, like distance of the planet from that star, the atmospheric density and composition, the nutrient base (terrestrial elements available to form the complex biochemical analogues of chlorophyll, etc.) and a myriad of other considerations.

Some plants may not even be photosynthetic; if you have a permanent cloud cover and can't see the sun, but you have a greenhouse effect going on, you might have thermosynthesis going on - that is to say, photosynthesis is an endothermic (consumes energy in chemical reaction and stores it) reaction, and it uses light because it is a plentiful and constant source of energy. In exobiology, we have to accept that ANY plentiful and constant source of energy is going to be adapted to and exploited by the resident life if it exists.

So, the less sunlight the planet actually receives, the more efficient the plant will become at harvesting what it gets, and if there are alternate sources of energy, extremophile life will adapt to harness that instead.

As for colour, it's almost entirely down to luck. There are a number of different photosynthetic compounds in existence, it's just that the dominant one on Earth happens to look green. But, your blue plants can form, and even exist on Earth today. So all in all what you want is possible, but it has very little to do with the 'colour' of the star the planet orbits when you get right down to it.

  • $\begingroup$ Are you sure it does "just happen" to look green? A Scientific American article suggested there were good evolutionary reasons for that, involving the reflection of green photons - "Whereas blue photons carry more energy than red ones, the sun emits more of the red kind. Plants use blue photons for their quality and red photons for their quantity. The green photons that lie in between have neither the energy nor the numbers, so plants have adapted to absorb fewer of them." $\endgroup$ – Astrid_Redfern Feb 20 '20 at 7:56

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