We might be able to spot evidence of life on other planets by looking out for the distinctive glow, allowing us to see evidence of aliens through Earth's telescopes, they say.
The alien worlds might be glowing with spectacular and beautiful colours, the researchers say – and that light show could direct us straight to any life that is on those planets.
The harsh ultraviolet light that is thrown out from red suns was once thought to mean instant death for life on other planets. But scientists say that it could actually be an important clue that allows us to see it: triggering a glow that emanates out into the rest of the universe and is visible from Earth.
"This is a completely novel way to search for life in the universe," said lead author Jack O'Malley-James, a researcher at Cornell's Carl Sagan Institute. "Just imagine an alien world glowing softly in a powerful telescope."
The phenomenon is called biofluorescence and the glow is formed as protection from the radiation that planets are hit with from their sun, according to the new research.
The discoveries are published in the Monthly Notices of the Royal Astronomical Society and promise a new way of looking for biosignatures – or indications of living things on other planets – that could help us finally discover alien life elsewhere in the universe.
"On Earth, there are some undersea coral that use biofluorescence to render the sun's harmful ultraviolet radiation into harmless visible wavelengths, creating a beautiful radiance," said co-author Lisa Kaltenegger, associate professor of astronomy and director of the Carl Sagan Institute. "Maybe such life forms can exist on other worlds too, leaving us a telltale sign to spot them."
Many of the planets outside of our own solar system are thought to orbit around M-type stars. Those are the most common kinds of stars in the universe, and regularly send out flares that hit the planets that orbit around them.
Those flares could be lighting up their planets with beautiful colours, astronomers suggest in the new paper. And those beautiful colours could be picked up by new telescopes either on Earth or sent up into space by humanity.
When the planets are hit by ultraviolet rays, they can be absorbed into longer and less damaging colours. That process is called photoprotective biofluorescence, and astronomers might be able to search for evidence of it to look for alien life.
"Such biofluorescence could expose hidden biospheres on new worlds through their temporary glow, when a flare from a star hits the planet," said Professor Kaltenegger.
To study the glow, scientists looked at similarly fluorescent pigments on Earth, which are commonly found in coral. That allowed them to model the kind of colours that other planets might emit, and allows them to simulate the strength and characteristics of any signal that would be detected on Earth, including whether it would be an indication of life.
It could now help astronomers examine planets we already know about, including Proxima b, a planet orbiting around our nearest neighbour star and a potential home for alien life. Researchers hope that could be used as a target to allow us to learn more about it from afar.
"These biotic kinds of exoplanets are very good targets in our search for exoplanets, and these luminescent wonders are among our best bets for finding life on exoplanets," O'Malley-James said.
Future telescopes could be developed to pick up exactly that glow as it is sent through the universe.
"It is a great target for the next generation of big telescopes, which can catch enough light from small planets to analyze it for signs of life, like the Extremely Large Telescope in Chile," Kaltenegger said.