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iLabs: Black Plants, Part II — NASA’s Take on Extraterrestrial Plant Colors

August 9, 2012

Revisiting the question of why aren’t plants black, Rob Gutro, of the Goddard Space Flight Center, wrote a 2007 article entitled:

NASA Predicts Non-Green Plants on Other Planets

In the article there is a discussion of why plants on earth are green. Scientists noted that plants seem inefficient as they did not use all the available green light. So apparently, not only are plants inefficient for not being black, but they don’t even seem to do a good job of using all the green light coming in:

“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.”

However, that’s not the whole story and there is an explanation for why more green light isn’t used on our planet:

“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.”

So viewing it this way, plants are actually VERY efficient. They don’t waste energy trying to use more light than they need. They’ve adapted to use the most prevalent wavelength, red light, and are doing fine with that. Anything more would be a waste of energy. So there’s no need for the plants to be black, at least on earth, because they’ve developed to maximize taking what they need from red light.

But what about other planets? Does this mean all planets would have green plants if they can support life? According to the NASA article, that’s not the case:

“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.”

Essentially, the color of the plants on other planets, will most likely depend on what light distribution its nearby star has, and what is the most prevalent wavelength or wavelengths that reaches the planet’s surface.

So from all of this as well as the info in Part I of this topic, it seems like plants understand better than us, that while you “could” in theory, get more energy from absorbing ALL wavelengths, and being a black plant, the reality is, it would be a gross INEFFICIENCY to do that.

For those of you who find the whole extraterrestrial-search-for-life topic interesting, NASA has a website devoted to Astrobiology, which from Wikipedia, is: “the study of the origin, evolution, distribution, and future of extraterrestrial life.”

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