View Full Version : Imagining Plants on another Planet

2007-Jun-25, 08:09 PM
If and when astronomers finally start discovering life on other worlds, they'll be wondering what kinds of lifeforms are there. They probably won't have plants as we know them, but there'll be some kind of life that converts light from the Sun into energy. ...

Read the full blog entry (http://www.universetoday.com/2007/06/25/imagining-plants-on-another-planet/)

Gliese 581 C
2007-Jun-25, 10:36 PM
Just a little nit-pick: You probably shouldn't be saying that the plant-life found on exoplanets will depends on light from "the Sun" when you're referring to other stars. "Their sun" or "their star" would be more appropriate.

2007-Jun-26, 01:58 AM
Plants here on Earth are green because of chlorophyll, which converts solar power into sugars for metabolism. But this isn't the best molecule. Ideally, you want something black, which absorbs all of the light.

So... why aren't plants black on Earth? If black is the best colour to absorb energy with, why stick with green?

2007-Jun-26, 02:57 AM
Mondo grass is black.

Ronald Brak
2007-Jun-26, 03:07 AM
There is a fairly big gap in the absorption of chlorophyll. Plants use carotenoids to fill some of this gap, but they still have a problem with 520 to 600 nanometers (green and yellow). There are bacteria that have pigments that fill most of this gap, but plants don't seem to use them. This might be because plants are stuck using the system they have and it's not really feasible for them to develop these pigments (sort of how insects are stuck with inefficient compound eyes) or it may be that their current system is the "cheapest" and it's not worth the investment of energy to use pigments to fill the gap.

And black leaves could overheat anyway. Plants around here often go to a lot of trouble to protect their leaves from midday heat.

There are pigments that can get energy from the near infrared which could be important for plants around very common red dwarf stars.

2007-Jun-26, 04:24 AM
Mondo grass is black.

Looks fairly green to me... (http://en.wikipedia.org/wiki/Mondo_grass)

Ronald Brak
2007-Jun-26, 11:14 AM
I've just been reading that chlorophyll apparently evolved convergently in several seperate linages. This suggests that carbon based life might often hit upon chlorophyll for photosynthesis on other worlds. Chlorophyll should be useful on worlds around worlds with smaller and larger suns than our own as it has two peaks where it absorbs light most efficiently. One peak for blue light and one peak for red. (With carontenoids absorbing some of the energy in the middle.)

Above me my flourescent tube converts ultraviolet light into visible light with phosphors and it is interesting to speculate that around bluer stars plants might use something similar.

2007-Jun-27, 11:07 AM
So... why aren't plants black on Earth? If black is the best colour to absorb energy with, why stick with green?

EDG. There's an interesting little side story there. I believe it was written up in Science News, my favorite little sci mag. The first pigmented plants performing photosynthesis were the brown and red algaes in the oceans. The red algae absorb strongly in the blue part of the visible spectrum (and reflect the red). The brown algae absorb strongly in the red part of the visible spectrum (and less in the blue). So, a soupy ocean mix had light for both.
Then chlorophyll appeared. It absorbs strongly at both red and blue wavelengths. It was able to starve the other algae of actinic radiation,by absorbing both ends of the spectrum simultaneously and "soon" dominated first the oceans, then the tidal zones,then as land plants the world. pete

2007-Jun-27, 06:58 PM
Looks fairly green to me... (http://en.wikipedia.org/wiki/Mondo_grass)

But the black mondo grass looks quite black.



2007-Jul-01, 06:44 AM
You would think that they could have used a better plant than egg plant to describ this story.