Alien plants purple instead of green? – Suggestion for biosignature search
Most stars in the Milky Way are smaller than the sun, and exoplanets receive less energy. This influences the colour of possible plants.
(Bild: Cornell University)
In the search for extraterrestrial life, it could be more effective to look for purple exoplanets rather than green ones. This is the opinion of a research team led by Lígia Fonseca Coelho from Cornell University in the US state of New York. The microbiologist bases her suggestion on so-called purple bacteria, which have ideal conditions to photosynthesize on exoplanets around the particularly common red dwarf stars. Their yellow, orange, brown, purple or red colouration is characteristic. If they did not have to compete with green plants, algae and bacteria, they could dominate many planets, the research group believes.
Purple is the new green
The term purple bacteria refers to microbiological organisms that photosynthesize on the basis of low-energy infrared light and do not produce oxygen. It is assumed that their energy production was the predominant form of photosynthesis among living organisms on Earth before plant photosynthesis, primarily based on chlorophyll, became established. This ensures that our world from space now looks green-blue and not red-blue. However, because there are mainly red dwarf stars in the Milky Way, it makes sense to look for other colours. The team adds that purple bacteria thrive in a wide variety of environments, and research objects have even been found in a pond on campus.
There is currently no technology to detect purple-coloured worlds, the team concludes. And even if such a coloured exoplanet were to be found, intensive work would have to be done to rule out alternative explanations. However, their work could serve as an opportunity to create a database of possible signs of extraterrestrial life. This is the only way to ensure that possible indications are not overlooked simply because researchers are not aware of all the work. We currently know of over 5600 exoplanets, more than 30 of which are considered Earth-like. Future telescopes will be able to study them in much greater detail. The research work on the purple bacteria was published in the Monthly Notices of the Royal Astronomical Society: Letters.
(mho)