Plant life under a red sun

[todofwar]

39 minutes ago, PB666 said:

But they can't help but absorb infrared, since almost all organics have absorption bands in the IR spectrum effectively they saturate the IR spectrum with absorption. If the spectrum shifts from green to a center in IR, it means to get the equivilent dose of Orange/Red or Red light in chlorophyll a or B the planet would have to be 2 or 3 times as close as our earth is the its star, much closer with a brown dwarf since output markedly drops.

For a plant or animal to absorb in the visible spectrum typically requires a photophore, the pigments are typically multiring systems in which the resonance stabilization of 4n+2 is spread across many atoms, there is many of these low energy orbitals with tiny shifts energy shifts from the lowest to the next to lowest state. For the smaller energy difference you want to capitalize upon, the larger the ring complex should typically be or the more exotic the metal in the complex. This is not an absolute rule but it is a general rule, The problem in the IR spectrum is that many things absorb, but nothing drops electrons or changes oxidation state (such as a chelated metal) So if you managed to have an agent that absorbs, it has to get to the IR before the all the mileau of it-just-got-hotter compounds absorb it. 

A deep red star or brown dwarf is going to have most of its energy produced in the IR spectrum. Cold brown dwarfs will produce no light they will look sort of purplish because of some UV/blue production and a trace of red, not going to support photosynthesis no matter how close the planet gets.

 

I think we might be saying the same thing? By red light, I mean the lowest energy visible light, not IR light. It's not possible to use IR light because there are no electronic transitions in the IR so you're not able to excite electrons for metabolism. Since, as you said, more of your light is coming in the IR region you need more total irradiance for the same amount of usable light energy in the visible or near IR (near IR would also probably not work, there are electronic transitions but it's hard to imagine the electron/hole pair persisting long enough to be useful). But, the IR light is still heating things up so by the time you have enough productive light you might be boiling away your oceans. 

[PB666]

37 minutes ago, todofwar said:

I think we might be saying the same thing? By red light, I mean the lowest energy visible light, not IR light. It's not possible to use IR light because there are no electronic transitions in the IR so you're not able to excite electrons for metabolism. Since, as you said, more of your light is coming in the IR region you need more total irradiance for the same amount of usable light energy in the visible or near IR (near IR would also probably not work, there are electronic transitions but it's hard to imagine the electron/hole pair persisting long enough to be useful). But, the IR light is still heating things up so by the time you have enough productive light you might be boiling away your oceans. 

Low energy red is below the excitation spectrum of chlorophyll b, however it is conceivable that the addition of addition aromatic side chains and rings could afford a lower spectrum. The problem is not just boiling oceans away, now that you are tidally locked, can you have a magnetic field to protect the entire atmosphere. The other question, its just my impression but the majority of red-stars, particularly the low-end of the spectrum are flare stars. If the star is very close to the planet the intense solar flares could actually sterilize the planet with electromagnetic bombardment from the flares itself, limiting life to deep vents and hydrothermal vents. Just read the wikis on the links below.

 

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Most flare stars are dim red dwarfs, although recent research indicates that less massive brown dwarfs might also be capable of flaring.^{[citation needed]} The more massive RS Canum Venaticorum variables (RS CVn) are also known to flare, but it is understood that these flares are induced by a companion star in a binary system which causes the magnetic field to become tangled. Additionally, nine stars similar to the Sun had also been seen to undergo flare events^[1] prior to the flood of superflare data from the Kepler observatory. - https://en.wikipedia.org/wiki/Flare_star

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In addition, red dwarfs emit most of their radiation as infrared light, while on Earth plants use energy mostly in the visible spectrum. Red dwarfs emit almost no ultraviolet light, which would be a problem, should this kind of light be required for life to exist. Variability in stellar energy output may also have negative impacts on development of life. Red dwarfs are often covered by starspots, reducing stellar output by as much as 40% for months at a time. At other times, some red dwarfs, called flare stars, can emit gigantic flares, doubling their brightness in minutes. This variability may also make it difficult for life to develop and persist near a red dwarf. Gibor Basri of the University of California, Berkeley claims a planet orbiting close to a red dwarf could keep its atmosphere even if the star flares.^[16] However, more-recent research suggests that these stars may be the source of constant high energy flares and very large magnetic fields, diminishing the possibility of life as we know it, though whether this is a peculiarity of the star under examination or a feature of the entire class remains to be determined. https://en.wikipedia.org/wiki/Red_dwarf

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Another fact that would inhibit habitability is the evolution of the Red Dwarf stars; as such stars have an extended pre-main sequence phase, their actual habitable zones would be for around 1 billion years in a zone where water wasn't liquid but in its gaseous state, so that terrestrial planets in the actual habitable zones, if provided with abundant surface water in their formation, would have been subject to a runaway greenhouse effect for several hundred million years. During such an early runaway phase, photolysis of water vapor and hydrogen escape to space could lead to the loss of several Earth oceans of water, leaving a thick abiotic O2 atmosphere. - https://en.wikipedia.org/wiki/Habitability_of_red_dwarf_systems

Dim red dwarves have the weight of evidence that disfavors complex life. However they could potentially have a status as a settled planets for an interstellar species and its companion species. The primary benefit for an interstellar species is a very long lived and stable star, The intense IR could be used advantageously such as in steam powered generation with no need for fossil fuels,etc. The problem is that all the planets so far around red dwarves are been superearths.

 

[PB666]

https://www.sciencedaily.com/releases/2016/05/160516125345.htm

[PB666]

http://gizmodo.com/life-in-red-dwarf-systems-may-be-rarer-than-we-thought-1778917829

Says that hydrogen helium burnoffs are not as rapid as should occur to support life. Not going to agree, just posting another point of view.