Scientists report on the Astrobiology journal that plants on other planets might not be green. They say the color of photosynthetic organisms depends on the makeup of the planet's atmosphere and on the type of star that the planet orbits:
“You have a particular spectrum which is affected by the star’s surface temperature, but once that light comes down through the atmosphere, the atmosphere filters that radiation,” said study team member Victoria Meadows of the Virtual Planet Laboratory (VPL) at Caltech.
For example, our Sun radiates most of its energy in the green part of the visible spectrum. But ozone molecules in the Earth’s atmosphere absorb much of this green light energy, allowing other colors, especially red, to filter through to the ground.
This could explain why chlorophyll absorbs mostly red and blue light and reflects green light, the researchers say.
“Ozone filters out some of the blue-green radiation, so there’s less of that available at the surface of the planet,” Meadows told SPACE.com.
Alternative explanations have also been proposed for the greenness of plants. One idea, called the purple Earth hypothesis, states that chlorophyll doesn’t absorb green light because it appeared after another pigment, called retinal, was already present and it had to settle for the “leftover” wavelengths that were not being absorbed.
The researchers reached their conclusions after analyzing 12 different kinds of light-sensitive pigments, including chlorophyll, that organisms on Earth use to harness the Sun’s energy.