The first extraterrestrial life we spot will probably be plant life, but what will it look like? There's a good chance it will be blue, purple, red or even black. A team of scientists examined what makes Earth plants green, then modeled the evolution of plants on worlds with different kinds of stars or atmospheres. The answers they came up with could help astronomers detect planets beyond our solar system with flora.
Plants use chlorophyll instead of some other pigment to drive photosynthesis because it is more efficient to absorb red and blue photons, based on the output of our sun and the light filtering attributes of our atmosphere. When they took these variables into account, the researchers found that planets around Class F and Class K stars, which are somewhat similar to our sun (Class G), would tend to have plants with either blue or red pigment, depending on the intensity of the starlight. Class M stars, aka red dwarfs, are cool stars that don't give off any ultraviolet radiation late in their lives. The relatively small amount of light available could result in black plants that try to absorb all the photons they can.
When advanced telescopes look at distant planets seeking life, they will need to know what colors to look for. If the planet has insufficient landmass, or all plants there live in the oceans, they will need to study the composition of the atmosphere with spectroscopy to determine if plant life may be present. Image by: Kenn Brown and Scientific American.
The Color of Plants on Other Worlds. [Scientific American]