Powerful flares from M-type stars (red dwarfs) — once thought to destroy life on their planets — might help uncover hidden biospheres; their ultraviolet radiation could trigger a protective glow from alien life called biofluorescence, according to a new paper published in the Monthly Notices of the Royal Astronomical Society.
M-type stars are the most common type of star in our Milky Way Galaxy and make up 75% of the stars in the solar neighborhood.
They are also excellent candidates for habitable zone terrestrial planet searches, due to the high frequency of rocky planets in the habitable zones of these stars.
M-type stars frequently flare, and when those ultraviolet flares strike their planets, biofluorescence could paint these worlds in beautiful colors.
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.
“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 Dr. Jack O’Malley-James, a researcher at Cornell’s Carl Sagan Institute.
“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. Maybe such life forms can exist on other worlds too, leaving us a telltale sign to spot them,” added Dr. Kaltenegger, Director of the Carl Sagan Institute.
The team used emission characteristics of common coral fluorescent pigments from Earth to create model spectra and colors for planets orbiting active M-type stars to mimic the strength of the signal and whether it could be detected for life.
“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,” Dr. O’Malley-James said.
“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,” Dr. Kaltenegger added.
Jack T. O’Malley-James & Lisa Kaltenegger. 2019. Biofluorescent Worlds – II. Biological fluorescence induced by stellar UV flares, a new temporal biosignature. MNRAS 488 (4): 4530-4545; doi: 10.1093/mnras/stz1842