When we think of naturethe first image that comes to mind is that of a green place with trees and plants. So it’s natural that when we look for Earth-like planets that could support life, we’re interested in planets that have green structures. We would rarely think about life related to other colors, and even less so with purple.
The main reason is the chlorophyllwhich represents a pigment capable of absorbing wavelengths of light such as blue and red, reflecting the green. The Sun itself has its maximum emission in green light lengths, but we observe it white or yellowish because we see the sum of all the colors. But life around other stars may have taken advantage of other wavelengths.
An article published in Monthly Notices of the Royal Astronomical Society studied the possibility that life on other planets is based on the color purple. The idea is based on purple bacteria that live in extreme environments on Earth. These bacteria could exist in environments around stars other than the Sun.
purple bacteria
Bacteria can exist in extreme environments even here on Earth. One of the bacteria that are of interest are those that use infrared radiation to carry out a process similar to photosynthesis. These bacteria have pigments in purple tones and that is why they end up being called purple bacteria.
They do not need to produce oxygen to survive and they can only depend on one band of the electromagnetic spectrum. Some studies show that they would have appeared when the Earth was still young and even before plants with chlorophyll emerged. Despite the name, There are also bacteria with red, orange and yellow tones.
Find a purple world
Since these bacteria would have a violet pigmentation most of the time, sA world dominated by them is expected to have a violet color, analogous to what happens on Earth where the color green is dominant because life depends on chlorophyll. Because of this characteristic of Earth, the search for life almost always focuses on planets with green characteristics.
However, before the possibility of bacteria dominating exoplanet environmentsthe idea is to search planets that have different colors. The objective is to be able to analyze the colors and chemical composition of exoplanets that are in a habitable zone. The habitable zone is the region around the star where liquid water is possible.
Searching for life
At the moment more than 5 thousand exoplanets have been confirmed by different global institutes and agencies. Of these 5,000 planets, only a few dozen have Earth-like characteristics. The main characteristic is the existence of the living area and also the existence of oxygen either molecules composed of carbon in the atmosphere.
According to the article, the group concludes that with purple bacteria it is possible to increase the range in which these searches are performed. With a greater reach, it is possible increase the number of planets on which life is possible. They can be considered planets with different compositions, colors and properties than Earth.
The Sun is no longer necessary
But perhaps the different characteristic that stands out the most is that the Sun itself could be different. Although the habitable zone changes for each type of star and this is considered when studying exoplanets, the Sun is related to the type of life on Earth. The way we see, photosynthesis itself and the evolution of life has the Sun factor.
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In the new paper, the researchers argue that because these bacteria are no longer dependent on sunlight and rely solely on infrared radiation, they would benefit around red dwarfs. Red dwarfs are cooler stars with greater emission in the red and some in the infrared, this would be a perfect environment for bacteria.
A new search for life
Perhaps we are about to further increase the possibilities of searching for life and thus increase the number of exoplanets of interest. She is serious a way of seeking a type of life completely different from ours but that still exists here on Earth in extreme environments such as the bottom of the sea.
Sources and references of the news:Coelho et al. 2024 Purple is the new green: biopigments and spectra of Earth-like purple worlds MNRAS
