Astronomers uncovered a new way of searching for life in the cosmos through harsh ultraviolet radiation flares from red suns that once helped to destroy surface life on planets.
"This is a completely novel way to search for life in the universe. Just imagine an alien world glowing softly in a powerful telescope," said lead author Jack O'Malley-James, a researcher at Cornell's Carl Sagan Institute.
"On Earth, there is some undersea coral that use biofluorescence to render the sun's harmful ultraviolet radiation into harmless visible wavelengths, creating a beautiful radiance. Maybe such life forms can exist on other worlds too, leaving us a telltale sign to spot them," said co-author Lisa Kaltenegger, associate professor of astronomy and director of the Carl Sagan Institute.
Astronomers generally agree that a large fraction of exoplanets beyond our solar system resides in the habitable zone of M-type stars, the most plentiful kinds of stars in the universe.
M-type stars frequently flare, and when those ultraviolet flares strike their planets, biofluorescence could paint these worlds in beautiful colours. The next generation of Earth - or space-based telescopes can detect the glowing exoplanets if they exist in the cosmos.
Ultraviolet rays can get absorbed into longer, safer wavelengths through a process called "photoprotective biofluorescence," and that mechanism leaves a specific sign for which astronomers can search.
"Such biofluorescence could expose hidden biospheres on new worlds through their temporary glow when a flare from a star hits the planet," said Kaltenegger.
The astronomers used emission characteristics of common coral fluorescent pigments from Earth to create model spectra and colours for planets orbiting active M stars to mimic the strength of the signal and whether it could be detected for life.
In 2016, astronomers found a rocky exoplanet named Proxima b -- a potentially habitable world orbiting the active M star Proxima Centauri, Earth's closest star beyond the sun, that might qualify as a target. Proxima b is also one of the most optimal far-future travel destinations.
"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.
Large, land-based telescopes that are being developed now for 10 to 20 years into the future may be able to spot this glow.
"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.
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