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Noclevername
2013-Nov-09, 06:43 PM
I don't recall where I heard it, but I somehow got the impression that some precursors of chlorophyll have been among the hydrocarbon molecules found in space rocks. I want to know because a story I'm working on involves finding life on an alien planet and I want to know what color to make the local autotrophs.

cjameshuff
2013-Nov-09, 07:28 PM
I don't recall where I heard it, but I somehow got the impression that some precursors of chlorophyll have been among the hydrocarbon molecules found in space rocks. I want to know because a story I'm working on involves finding life on an alien planet and I want to know what color to make the local autotrophs.

I seem to recall that porphyrins were detected in interstellar dust.

As for the color, it could be anything. Some examples of a porphyrin pigment here: http://www.rsc.org/Publishing/ChemTech/Volume/2010/04/twin_action.asp

Noclevername
2013-Nov-09, 09:06 PM
Thanks. It seems I have a spectrum of colors to choose from. :)

Swift
2013-Nov-09, 10:11 PM
There was a Scientific American article I recall about what color alien foliage might be and they were relating it to the spectrum of the star the planet is orbiting; that plants would optimize to maximize absorption of light. As cjameshuff shows in that article, there are a wide variety of compounds that would work.

Spacemad
2013-Nov-09, 10:49 PM
There was a Scientific American article I recall about what color alien foliage might be and they were relating it to the spectrum of the star the planet is orbiting; that plants would optimize to maximize absorption of light. As cjameshuff shows in that article, there are a wide variety of compounds that would work.

I also remember having read that article some time ago as, apart from reading & posting on forums related to space exploration, I'm very much into gardening! (A strange mixture I suppose - with my head in space & my hands in the soil! :D) So it was an article that interested me, being as it were, a mixture of my two greatest interests!

cjameshuff
2013-Nov-09, 11:18 PM
There was a Scientific American article I recall about what color alien foliage might be and they were relating it to the spectrum of the star the planet is orbiting; that plants would optimize to maximize absorption of light.

But if they did that, they'd be black. Here on Earth, they actually picked a pigment that reflects in the most intense part of the spectrum. This may have been for control of temperature, or it may just be that green chlorophyll plants developed a particularly efficient metabolism that is also highly specific to chlorophyll...a local optimum from which it is very difficult to reach a more global optimum. It might also be that there's little pressure to optimize light absorption, since plant metabolism is generally limited by respiration instead.

So unless it's a particularly terrible fit to the star's spectrum, pretty much any color may do.



As cjameshuff shows in that article, there are a wide variety of compounds that would work.

And I think that's actually just one compound with different metal ions trapped in the porphyrin ring, at different temperatures. An impressively wide range of colors...

Delvo
2013-Nov-09, 11:52 PM
Maximizing absorption at the wavelength the local star produces the most of isn't how chlorophyll became dominant here. In fact, the wavelengths chlorophyll reflects the most are generally around the highest part of the solar output graph, although that's not a very steep-sloped so I wouldn't call it a "peak". Nobody knows why.

One theory I've seen involves evolutionary pressure away from absorbing too much energy and overheating. Another is that the answer must lie in differences in efficiency in some other biochemical process related to pigments, such as the resources needed to produce them, the molecules' average duration before falling apart and needing replacement, the same considerations for some other non-pigment compounds that are also involved in the overall system around the pigments, and harmful compounds getting produced as side effects and how to deal with them. Another theory is that the original green ancestors of chloroplasts lived some distance below the surface of the water, originally getting out-competed by other photosynthesizers above them which acted as a filter, and so the green ones developed chlorophyll to absorb the peak wavelengths in the light that was left over; then they became dominant later for unrelated reasons, after having already gotten stuck on a green pigment.

I don't buy that last one, not just because it sounds like the kind of idea that would be come up with by someone who isn't aware of how flexible and "creative" evolution can get, but because plants DO use other pigments too. (In my part of the world, you can even see them for several weeks every October and November, when chlorophyll levels decrease.) Even if coming up with a whole new pigment is too much to expect, that doesn't mean adjusting the ratios of the ones that are already there is. And different plant species actually do come in slightly different shades of green based at least partially on the ratios of those other pigments, so we know they can and do get adjusted, which must mean that the explanation of the cause must be some benefit that still applies now, not just eons ago.

Swift
2013-Nov-10, 04:07 PM
And I think that's actually just one compound with different metal ions trapped in the porphyrin ring, at different temperatures. An impressively wide range of colors...
To me a porphyrin ring with a different metal ion is a different compound, but maybe I'm nitpicking.

Noclevername
2013-Nov-11, 10:14 AM
Would anyone happen to have a list of the light absorption frequencies for the various porphyrins (or at least the most common)? It's a long shot, I know, but it doesn't hurt to ask.