Red hills of distant planets
Imagine you are standing in a jungle. You are surrounded by lush healthy foliage; a sea of green, perhaps punctuated by the occasional flower in a contrasting hue.
Now imagine yourself on a distant planet with similarly abundant plant life. What would it look like? It might well be scarlet or vermilion, rather than verdant.
Most Earthly plants are green because contain the pigment chlorophyll, which reflects green light and absorbs red and blue light. The energy from the light absorbed by chlorophyll is used for photosynthesis – the conversion of carbon dioxide into sugars and other organic compounds.
Along with green light, chlorophyll also reflects near-infrared light – called the “red edge” – which is invisible to the human eye, but can be detected remotely using near-infrared sensitive cameras. Currently satellites use such systems to remotely monitor the health of vegetation on Earth. That ability makes chlorophyll detection a reasonable potential molecular signature of extraterrestrial life.
But it may wrong to assume that plant life (or the equivalent) on other planets will necessarily be green.
Once the light from our Sun is filtered through the ultraviolet light-absorbing ozone layer, more photons at the red end of the spectrum reach the Earth’s surface than at other wavelengths. It makes sense, then, that Earthly plants primarily use red light.
A planet that orbits a star hotter than our own sun or that has an atmosphere that absorbs a different range of wavelengths than Earth’s, might have a greater abundance of blue photons than red photons on its surface. Orange or red plants might dominate there.
And Washington University chemist Robert Blankenship has suggested that alien plants might use black pigments that absorb all visible wavelengths of light. That might be necessary for plants on planets orbiting cool red dwarf stars.
The only plant color that is considered to be unlikely is bright blue, since that would mean that high energy blue light is being reflected from the leaves, rather than utilized. But I consider that to mean that blue plants are unlikely, not impossible.
So how are plants portrayed in science fiction?
H.G. Wells’ invaders in the War of the Worlds carried invasive red-colored weeds to Earth. That fits nicely with the notion of Mars as the “red planet”, but isn’t really based on biology – not too surprising, since photosynthesis was not well understood in the early 20th century.
Other SF novels do include strange and alien plants, but to the best of my recollection they generally have green foliage. It seems like a missed opportunity to increase the strangeness of alien worlds.
I’d love suggestions for SF stories that do include alien non-green plants in the comments.
Additional Reading
- Cosmic Variance: “The Red Edge“
- Seager S. et al. “Vegetation’s Red Edge: A Possible Spectroscopic Biosignature of Exraterrestrial Plants” Astrobiology 5: 372-390 (2005) DOI: 10.1089/ast.2005.5.372 (subscription required to access full article)
- Goddard Space Flight Center News: NASA Predicts Non-Green Plants on Other Planets
- NASA GISS: Science Briefs: The Color of Life, on Earth and on Extrasolar Planets
- Astrobiology News: Pondering Alien Plants
- Astrobiology News: Fall Colors on Alien Worlds
Image (top): “Jungle Green” by Flickr user JoetheLion, recolored
Image (bottom): “Jungle Green” by Flickr user CaptPiper, recolored
Very nice: plants are near and dear to my heart, after all.
There are plenty of books with oddly-colored plants, but I can’t think of any that are colored for physiological reasons rather that to look cool.
Frederik Pohl’s, “Jem” had dark colored plants suitable to it’s red dwarf sun, as did the collaboration “Medea”, that Pohl spun Jem off from.
http://en.wikipedia.org/wiki/Medea_(planet)
Perelandra by C.S. Lewis had plants in a wide variety of color, though i don’t think there was science behind that.
I’m sure a significant minority of what i’ve read include plants of various colors, but i can’t bring any others positively to mind, since it’s usually not a very important detail. Sometimes it’s just a random description.
While it’s somewhat disappointing to find the same old green plants, there are some good reasons why they are prevalent. Who known how often it’s good reasoning or simply laziness the bring us so many green plants.
Most sci-fi planets where stories take place are reasonably habitable for humans, since like it or not humans are at least some of the central characters in most sci-fi.
In the past, though not so much recently, planets around red dwarves were assumed to be uninhabitable by human-kind, due to the extreme conditions of tidally locked worlds. And larger stars in the blue-to-ultra violet range are supposed to put out dangerous levels of harder radiation. In other words (at least according to a lot of scientists) the planets humans will tend to be on will tend to have yellow suns or close colors.
Additionally alien foods are unlikely to be usable for earth-life, without of replicator technology, people will tend to inhabit planets where they can grow earth crops.
Of course even on Earth there are exceptions to the rule of green, there are redish and purpleish, and whitish leaved plants among my mother’s garden. Apparently other colors work, even if there’s still chlorophyl underneath.
The Medea story collection sounds very cool. I’m putting that on my “want to find a copy” book list.
That’s a good point that Earthly plants aren’t all green. My next door neighbors have a plum tree with lovely purple-red leaves, for example.
I could imagine an Earth-like planet with a different evolutionary history ending up with a higher proportion of reddish or orangeish flora than we have here on Earth.
Tastes differ, of course. Personally, I found the Medea collection completely underwhelming (and eventually annoyingly sloppy as both science and fiction, despite its interesting and the famous names associated with it.
I dropped a word there! I meant to say “despite its interesting premise”.
I agree that that Media is not remarkable great sci-fi. I think that perhaps that the collaboration wasn’t entirely successful, i.e. some of the various authors’ ideas didn’t mesh. Some of them might have written better stories if they weren’t constrained by stuff that other authors conributed to the world.
The parts i liked more was the transcript of the brainstorming session between all these big names. It’s fun to see how they think and interact.
The Eye Altering, by Ursula Le Guin. A wonderful novelette that not only has differently colored vegetation the evolved under a red sun, but also shows the vision of the human settlers shifting to fit their new home.
I had forgotten about “The Eye Altering”! That’s a great example.
Bujold’s Barrayar has reddish-colored plant life. And Rosemary Kirstein’s world has red grass and black grass, with the red grass being sort of edible to wildlife, and the black grass being toxic.
Posts like this are great on a number of levels. The joy of science, the potential for better informed fiction in the world, and the expansion of my reading list. Brilliant!