Ultraviolet Flares from M-Type Stars Might Help Uncover Hidden Biospheres

Astronomers who search for life on faraway planets may have to look for the glow.

Once it was considered that severe ultraviolet radiation flares from red suns kill life on the surface of planets. However, the same flares could help unravel hidden biospheres. A new study led by Cornell University proposes that radiation from such flares could set off a protective glow from life on exoplanets known as biofluorescence.

The study, titled “Biofluorescent Worlds II: Biological Fluorescence Induced by Stellar UV Flares, a New Temporal Biosignature,” was published in Monthly Notices of the Royal Astronomical Society on August 13^th, 2019.

“This is a completely novel way to search for life in the universe. Just imagine an alien world glowing softly in a powerful telescope,” stated Jack O’Malley-James, a researcher at Cornell’s Carl Sagan Institute and lead author of the study.

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.

Lisa Kaltenegger, Associate Professor of Astronomy and Director, Carl Sagan Institute, Cornell University

Kaltenegger is the co-author of the study.

In general, astronomers concur on the idea that a large fraction of exoplanets—planets located outside the solar system—dwell in the habitable zone of M-type stars, the most abundant types of stars in the cosmos.

M-type stars flare very often. When the ultraviolet flares hit their planets, biofluorescence could paint these realms in splendid colors. The future generation of space- or Earth-based telescopes have the ability to track the glowing exoplanets, if they occur in the universe.

By a process known as “photoprotective biofluorescence,” ultraviolet rays could get absorbed into safer, longer wavelengths. This mechanism leaves a particular sign that astronomers can look for.

“Such biofluorescence could expose hidden biospheres on new worlds through their temporary glow, when a flare from a star hits the planet,” stated Kaltenegger.

The emission properties of common coral fluorescent pigments from Earth were leveraged by the astronomers to develop model spectra and colors for planets that orbit active M stars to simulate the signal’s strength and if it could be detected for life.

In 2016, a rocky exoplanet called Proxima b was discovered by the astronomers. This exoplanet was a potentially habitable planet that orbited the active M star Proxima Centauri, star closest to the Earth beyond the sun—which might qualify as a target. Moreover, Proxima b is one of the most preferred 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.

Jack O’Malley-James, Researcher, Carl Sagan Institute, Cornell University

This glow might be spotted by huge, land-based telescopes currently being developed for one to two decades into the future.

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.

Lisa Kaltenegger, Associate Professor of Astronomy and Director, Carl Sagan Institute, Cornell University

The study was funded through the Simons Foundation.