Algae, moss and bacteria can all survive and grow in the light produced by a red dwarf star, according to experiments on Earth. This boosts the idea that planets around red dwarf stars like TRAPPIST-1 could host life.
The most promising exoplanets for life orbit stars that are smaller and cooler than our sun, so they radiate different profiles of light. For instance, a star like TRAPPIST-1 would give out more infrared light. But we know little about how this would affect life.
Last year, at the University of Padua in Italy and her colleagues tested how organisms from Earth might fare under simulated starlight by placing several types of cyanobacteria (also known as blue-green algae) in a starlight generator consisting of 273 controllable LEDs, which could mimic sunlight or red dwarf light.
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The cyanobacteria, which are efficient at photosynthesising 鈥� getting energy from sunlight 鈥� and can work in low and redder light, .
This is important, La Rocca told the in Granada, Spain, on 19 September, because cyanobacteria were crucial in making Earth habitable for other organisms. 鈥淭hey totally changed our planet, being responsible for the start of oxygen production,鈥� she said.
Now, La Rocca and her team have put other types of organisms in the simulator that aren鈥檛 as good at harvesting light as the cyanobacteria, such as the microalgae Chlorella vulgaris and Chromera velia, as well as a moss, Physcomitrella patens, to test how they might fare.
Although all the organisms were able to grow under the artificial red dwarf light, most of them grew slightly less than they did under the simulated sunlight 鈥� except for one species, C. velia, which grew more.
La Rocca and her team also noticed that under artificial starlight, the moss failed to grow certain reproductive structures that are normally present under sunlight. 鈥淢aybe the organism can grow but no longer reproduce. This will deserve more investigation,鈥� La Rocca told the conference.
The team also tested how much oxygen was produced by each species of cyanobacteria under different simulated lights and found that they would all contribute to an atmosphere under red dwarf starlight.
Next, La Rocca鈥檚 team hopes to test how much oxygen the more complex organisms produce, and to make mathematical models to evaluate the possibility of these organisms existing on planet surfaces.
Using organisms from Earth to evaluate how habitable alien star systems could be isn鈥檛 straightforward, says at Johns Hopkins University Applied Physics Laboratory in Maryland. 鈥淚t鈥檚 very difficult to imagine life in other star systems evolving exactly how it evolved on Earth,鈥� he says. 鈥淪o while it鈥檚 interesting to see how a photosynthetic organism might respond to different starlight, those organisms are still very complex, and it took billions of years of evolution on Earth to get them.鈥�
However, the work gives us a baseline for hypotheses to test when looking at the light spectra that come from worlds orbiting different stars, says Phillips.
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