If you look up at the sky tonight and see something glowing, congratulations! You might just have discovered E.T.
In a new paper, scientists say alien life might give itself away by giving their planet a fluorescent glow.
"This is a completely novel way to search for life in the universe," said lead author Jack O'Malley-James, of Cornell University's Carl Sagan Institute, named for the famed astronomer.
"Just imagine an alien world glowing softly in a powerful telescope."
The theory is this: M-type stars are the most common in the universe, but frequently bathe their planets in destructive flares of UV rays. Normally this would wipe out life before it could really get started, but there are creatures right here on Earth that have figured out how to block UV rays naturally.
"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, also of the Carl Sagan Institute.
"Maybe such life forms can exist on other worlds too, leaving us a telltale sign to spot them."
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Most UV rays that reach Earth are blocked by the ozone layer. But if a planet didn't have such a shield, its life could evolve to handle UV rays in other ways.
O'Malley James and Kaltenegger hope telescopes currently in development will be strong enough to detect biofluorescent glows in 10 or 20 years.
"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," said Kaltenegger.
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An early target will be rocky planet Proxima B, which orbits Proxima Centauri, the closest star to Earth that isn't the sun.
"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," said O'Malley-James.
Their paper was published in journal Monthly Notices of the Royal Astronomical Society.