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Alien life may thrive on purple planets, new study of extreme bacteria suggests




To find life on far-off planets, astronomers may need to look for pinpoints of purple.

New research unravels the light signals that are likely to come from worlds where oxygen and sunlight are in short supply — which is likely the case for many exoplanets discovered so far.

On Earth, the dominant color signal for life is green, thanks to bacteria and plants that use green chlorophyll to transform visible sunlight into energy. On a planet orbiting a smaller, dimmer star, however, organisms are more likely to thrive if they can run their metabolism on invisible infrared light.

Infrared-powered bacteria exist in many niches on Earth, especially in places where sunlight doesn't penetrate, like murky marshes or deep-sea hydrothermal vents. In a new study published April 16 in the journal Monthly Notices of the Royal Astronomical Society, Lígia Fonseca Coelho, an astrobiologist at Cornell University, and her co-authors grew a sample of these bacteria, measured the wavelengths of light they reflected, and simulated what those light signatures would look like on various far-flung worlds.

Related: Little Green Men? Nope, Extraterrestrial Life May Look More Like Pasta.

Telescopes such as the Extremely Large Telescope, which is under construction in Chile, and the Habitable Worlds Observatory, which is still in the planning stages, will be able to search for these light spectra, the study researchers said.

"We need to create a database for signs of life to make sure our telescopes don't miss life if it happens not to look exactly like what we encounter around us every day," co-author Lisa Kaltenegger, a Cornell University astronomer and director of the Carl Sagan Institute, said in a statement.