The carotenoids (pigments that give color to vegetables like tomatoes and carrots) in certain purple bacterial species can tap into the energy of visible light, while bacteriochlorophylls (BChl) ‘a’ and ‘b’ can use the infrared (IR) band for harvesting energy. As a result, there’s theoretically a much higher chance of finding these bacterial species on a distant planet orbiting an M-type (aka red dwarf) star that’s cooler compared to our sun, a G-type (aka yellow dwarf) star.
With a reasonable probability of finding such bacterial life forms on alien planets, or at least with the intention of not missing their biosignatures, a team of scientists at Cornell is creating a database of colors and chemical signs for a wide range of organisms.
The team has collected over 20 purple sulfur and purple non-sulfur bacteria, and after assessment of their bio-pigments and light characteristics, they developed models of Earth-like planets with diverse climatic conditions and cloud cover. To put it more specifically, the team analyzed the reflectance of purple bacteria in a variety of oxygen-rich and oxygen-deprived conditions. When the data was fed into the model of these extraterrestrial environments, both hydrated and arid purple bacteria exhibited vividly colored life signs.
