Research says that life may survive around even the tiniest stars

A starlight simulator (left) and when illuminated (right). Credit: La Rocca, et al

The most crucial chemical process for life on Earth is undoubtedly photosynthesis. It is the mechanism through which plants convert sunlight into energy that they can use. It allows plants to create carbohydrates that they can consume (and that we can eat when we harvest them), while also producing oxygen as a byproduct. Because of photosynthesis, the Earth's atmosphere contains around 20% oxygen. Without photosynthesis, there would be no life on Earth as we know it.

It is also the cause for the green color of many plants. Most plants employ chlorophyll in their photosynthetic process, which reflects green light while absorbing red and blue light. That seems strange given that the sun emits the most powerful light in the green portion of the spectrum. Retinal is a photosynthetic molecule that absorbs green and reflects red and blue light. Most plants would be purple if they employed retinal instead of chlorophyll. Some bacteria employ retinal, but it turns out that chlorophyll is more effective in sunlight, so it provides more bang for your money overall. It's likely that in the beginning, life utilized retinal, a simpler chemical, before learning how to employ chlorophyll.

Photosynthesis, of course, developed to take use of a brilliant yellow star that produces the majority of its light in the visible spectrum. However, sun-like stars account for fewer than 8% of the main sequence stars in our galaxy. In contrast, red dwarfs account for 75% of main sequence stars. The great majority of possibly habitable planets circle a red dwarf, according to statistics. Furthermore, red dwarfs are significantly smaller and colder than our sun. The majority of the light they emit is infrared. Infrared light is pleasant and warm, but does it have the punch necessary to power photosynthesis? A recent study attempted to answer this question.

The spectrum of the sun compared to that of an M-class red dwarf. Credit: T Roger/Europlanet 2024 RI

They constructed a starlight simulator to do this. It's an LED array designed to replicate the spectrum of a red dwarf. The system can simulate the spectra of numerous sorts of stars, but because red dwarfs are so prevalent, they initially analyzed them. They then generated an atmosphere like that of an early habitable Earth, added microorganisms, and lit it with synthetic starlight.

They began with cyanobacteria, which were among the earliest creatures on Earth to manufacture oxygen through photosynthesis. They are very adept in surviving in difficult situations. Because the cyanobacteria survived and developed in the infrared glow of a red dwarf, the researchers repeated the experiment with red and green algae. They both thrived as well. So, even though red dwarfs do not provide the sort of light that spurred photosynthesis' development, terrestrial animals may exist under a red dwarf sun. This is fantastic news for everyone looking for alien life.

Of course, there are other issues with red dwarfs that might make life impossible in their worlds. The stars are known to release intense flares that might deplete the atmospheres of nearby worlds, and they may lack the basic supplies required for sophisticated creatures. However, it is a fantastic research that has shed some light on our knowledge of life on distant worlds.

Journal Information: La Rocca, N., et al, Responses of eukaryotic photosynthetic organisms to simulated M-dwarf star light. Europlanet Science Congress EPSC2022 (2022).