Friday, April 13, 2007

The Color of Alien Flora

Apparently the vegetable kingdom in Mars, instead of having green for a dominant colour, is of a vivid blood-red tint. At any rate, the seeds which the Martians (intentionally or accidentally) brought with them gave rise in all cases to red-coloured growths. Only that known popularly as the red weed, however, gained any footing in competition with terrestrial forms. The red creeper was quite a transitory growth, and few people have seen it growing. For a time, however, the red weed grew with astonishing vigour and luxuriance. It spread up the sides of the pit by the third or fourth day of our imprisonment, and its cactus-like branches formed a carmine fringe to the edges of our triangular window. And afterwards I found it broadcast throughout the country, and especially wherever there was a stream of water.
~ H.G. Wells, The War of the Worlds

Exotic extraterrestrial foliage has been a science fiction staple since Wells' described the invading red plants of Mars in 1898. While red plants are colorful, natch, they don't necessarily have any basis in biology. Fortunately for people who like bio-accuracy in their science fiction, NASA biometeorologist Nancy Kiang and colleagues have published an article that predicts the color of plant life on extrasolar planets based on the type of star the planet orbits and the predicted planetary atmosphere.

The plant color we see is determined by the wavelength of light reflected by their leaves. Typical green plants absorb photon-rich red light and high-energy blue light and reflect the unused green light. Light absorbing pigments such as chlorophyll capture the photons' energy, which is then used to convert carbon dioxide and water into sugar. Based on the current understanding of that process of photosynthesis in terrestrial plants and bacteria, the NASA-lead research team believes that plants can come in many colors - except bright blue.

The news@nature.com article conveniently provides a star type - plant color guide:

Star typePrimary color light used for photosynthesisPlant Colors
Hotter than the sunbluewhite (to prevent blue-light overdose) or green-yellow-orange-red
Like the sun redgreen-yellow-orange
Cooler than the sunredgreen-yellow-orange
Red dwarf all light,black

infrared, grey-white

or yellow-redpurple, many other colors

It looks like red is an unlikely color for plants growing in our solar system. But if the invaders were from a planet orbiting Sirius, that's another story.

Tags: , Image from the NASA article.

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