April 11, 2007 / 6:19 PM / 12 years ago

New hue: Plants on other planets may be yellow, red

CHICAGO (Reuters) - The same rules that make Earth plants green may make non-Earth plants yellow, red or green — but likely not blue, NASA scientists said on Wednesday.

An artist's illustration shows possible colors of foliage on extra-solar planets. The same rules that make Earth plants green may make non-Earth plants yellow, red or green -- but likely not blue, NASA scientists said on Wednesday. REUTERS/Caltech illustration by Doug Cummings/Handout

They said their findings — which look at how plants absorb and reflect different types of light — may help narrow the search for life on planets beyond our solar system.

And, as a bonus, they may have answered a basic question about life on Earth.

“We’ve uncovered maybe the best explanation of why plants are green,” said Nancy Kiang, a NASA biometeorologist who led the study, which appears in the journal Astrobiology.

Understanding plant colors on other planets is important as scientists prepare for new information to be generated from giant space telescopes planned by NASA and the European Space Agency to study Earth-sized planets orbiting other stars.

“We can guess the plausible range of colors they might be,” said Vikki Meadows, an astrobiologist the California Institute of Technology who heads NASA’s Virtual Planetary Laboratory.

Meadows and a host of scientists from different disciplines first studied how light is absorbed and reflected by plants and some bacteria on Earth.

That led to computer model for predicting the color of plants on other planets and new insights about plants on Earth.

Chlorophyll in plants takes light from the sun and converts it into energy through a process called photosynthesis.

Scientists have long known that most plants on Earth absorb more blue and red light and less green light, but they have not understood why.

It turns out that more red light reaches plants on Earth, and blue light is the easiest to absorb. So plants make most efficient use of these two, and that leaves green light as largely superfluous.

“They don’t absorb the green because they have more than enough light from blue and red. They just don’t need green,” Kiang said.

As a result, plants reflect away relatively more green light, which is why plants appear green.

“It turns out plants are actually using the best light there is,” Kiang said.

On other planets, where other colors of the light spectrum might dominate, the plants might soak up more green or even more blue light and reflect back whatever is not needed for energy.

The scientists believe the same rules will apply on Earth-like planets in other solar systems.

“It turns out that photosynthesis is one of those things that is likely to be common. If we look for life on other planets, we will try to look for signs of photosynthesis,” Meadows said.

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