Light from our closest star Alpha Centauri could reveal signs of alien life on its planets
The light coming from distant solar systems could reveal the existence of plants growing on other planets, according to astronomers.
Scientists have found that the pigments in the leaves of plants and other photosynthetic organisms reflect coloured light in peculiar ways, producing a distinctive fingerprint.
This means it may be possible to filter out other light coming from distant stars to reveal only light that has been reflected by living plants on a planet’s surface.
The findings could provide a new way of finding alien life beyond our solar system that does not rely upon detecting radio signals from other intelligent life forms.
Instead, astrobiologists may be able to pinpoint planets orbiting other stars where photosynthetic organisms exist by looking for coloured visible light that has been polarised in specific ways.
This could also help to identify planets which may be habitable by humans – photosynthesis produces oxygen as a key by product.
The researchers hope to use the technique to search for signs of life on the planets orbiting our nearest stars including Alpha Centauri A and B, which are 4.37 light years from Earth.
Writing in the International Journal of Astrobiology, Professor Sventlana Berdyugina, from the University of Freiburg in Germany and a scientist at the University of Hawai’s Nasa Astrobiology Institute, and her colleagues said: ‘Photosynthesis, which provides organisms with the ability to use light as a source of energy, emerged early in the evolution of life on Earth.
‘The ability to harvest such a significant energy resource could likely also develop on inhabited exoplanets.
‘Our results demonstrate that linearly polarized spectra provide very sensitive and rather unambiguous detection of photosynthetic pigments of various kinds.
‘Our work paves the path towards analogous measurements of microorganisms and remote sensing of microbial ecology on the Earth and of extraterrestrial life on other planets and moons.’
Plants, bacteria and algae use a variety of photosynthetic pigments to help them capture energy from the sun and use it to convert Carbon dioxide gas and water into oxygen and sugar.
In green plants, chlorophyll absorb blue to red light and reflect a small amount of green light. They also reflect infrared light.
In other organisms, such as in red algae, other pigments use different wavelengths of light for photosynthesis.
By measuring the light reflected off these photosynthetic pigments, the researchers found the coloured light tended to bounce off with a particular polarisation.
Each biopigment has its own coloured fingerprint in the polarised light. These differ from minerals, rock and seawater, the scientists found.
As non-reflected light moves in all directions and is not polarised, it means it would be possible to filter out the other light from stars millions of times brighter than the planet orbiting them to search for signs of plant life.
The scientists used models to show that flight reflected off distant Earth-like worlds elsewhere in the galaxy would enable them to spot photosynthetic signatures on the planets.
The researchers said it may even be possible to search for these signs using existing telescopes on Alpha Centauri but it could be extended further using more powerful telescopes in the future.
Unfortunately so far only one star in the Alpha Centauri system, which is a binary star system of two stars orbiting each other, has been found to have a planet.
The small planet was discovered orbiting Alpha Centauri B, but it is around ten times closer to its star than Mercury is to our sun, meaning it is unlikely to have any water or an atmosphere.
However researchers have seen tantalizing hints of other planets around the stars, which could be better candidates for life.