The colour of alien plants will be determined by the wavelengths of light that reach them.
Credit: Caltech
SYDNEY: Planets outside our Solar System may have orange, yellow, red or even black plant life, according to a new NASA study.
Scientists with the U.S. space agency have studied how light is absorbed and reflected by plants on Earth, to predict what vegetation might look like on planets which have different atmospheres and orbit different stars.
Published in the latest issue of the journal Astrobiology, the find may prove valuable in helping scientists recognise life on extrasolar planets.
According to Nancy Kiang, lead author of the study and bio-meteorologist at NASA's Goddard Institute for Space Studies in New York, the light that hits the surface of other planets is likely to be very different to the sunlight we see. This is because not all stars emit the same distribution of wavelengths of light and not all atmospheres filter light in the same way.
"Photosynthesis produces global signatures of life that can be seen from great distances," said Kiang, making it particularly useful for detecting the presence of life on other worlds.
Scientists already knew that plants on Earth rely mostly on abundant red light for photosynthesis. Hence the green colour of the chemical chlorophyll in plants, which absorbs most light in the red part of the spectrum. Assuming that extraterrestrial planets rely on light from other stars for their survival, Kiang has predicted that - if they exist - they will absorb and reflect different colours.
To investigate the idea, Kiang worked alongside colleagues at the California Institute of Technology's Virtual Planetary Laboratory (VPL) in Pasadena. The researchers used computers to model Earth-sized planets and the light reaching their surfaces from the stars they would orbit.
They focused on planets that would be habitable to the kind of life that we have on Earth - and therefore those that orbited their stars at a distance warm enough to have liquid water.
By looking at the changes in light through different atmospheric compositions, they were able to calculate what stellar light would look like at the surface of other planets, which in turn, enabled them to determine what colours would be most favourable for photosynthesis.
"We can identify the strongest candidate wavelength for the dominant colour of the photosynthesis on another planet," said Kiang.
She said that stars brighter than our Sun would emit more blue and ultraviolet light. In response, vegetation on orbiting planets may contain yellow- or orange-looking photosynthetic chemicals to best absorb those colours.
If the atmosphere of those planets were high in oxygen, they would likely form an ozone layer, which obstructs ultraviolet light. On Earth our ozone layer allows mostly red light through, but the light from a brighter star would be filtered so that more blue light makes it to the surface. As a result plants might evolve a type of photosynthesis that absorbs blue and green light, and reflects yellow, orange and red, she said.
In contrast, stars slightly weaker than our Sun would emit a solar-like light to the surface of extraterrestrial planets - so its vegetation might look similar to that on Earth. Planets in the wake of very dim stars could even have vegetation that is black, to absorb as much light as possible, suggest the researchers.
"This work will help guide designs for future space telescopes that will study extra solar planets, to see if they are habitable, and could have alien plants," said astronomer Victoria Meadows, who heads up the VPL in Pasadena.
It's too early to know for certain what plant life on extra solar planets might look like, but this study will help guide astronomers in their search, commented Jeremy Bailey, from the Australian Centre for Astrobiology at Macquarie University in Sydney.
Astrobiologists had imagined that plants on other planets might look similar to plants here on Earth, but this study "indicates that we can't assume what happens on other planets is what happens on Earth," added Bailey.
Its about time...
It finally took NASA and ACA scientists over 40 years to discover what uncle Martin (in My Favorite Martian)had already stated all of those years ago. In fact, in one episode he confirms that vegetation on Mars is pink!