The most abundant stars in the galaxy constantly douse their planets with dangerous flares. These dramatic events unleash radiation and charged particlescan that decimate protective atmospheres and destroy any potential life. As a result, even when stars are surrounded by water-rich worlds, scientists wonder whether life could ever thrive in such harsh conditions.
Now new research suggests a rather whimsical form of protection: Hypothetical aliens could shield themselves by shifting the harmful radiation to something more benign, creating a ghostly glow that the next generation of telescopes might even be able to detect. That's right: glow-in-the-dark aliens.
On Earth, numerous plants, animals, and even minerals light up their surroundings. Some, like fireflies, create their own illumination through an ingenious chemical process known as bioluminescence. Others work with whatever comes their way, transforming the sun’s light by reflecting it at different wavelengths in a process known as biofluorescence. Creatures from snails to jellyfish to deep-sea worms use these processes to light their way and attract prey.
But there are other potential uses for harnessing the power of light. If life on a planet around an active star evolved the ability to glow, it could mitigate the damage it might otherwise suffer from the flares. "It would be taking the harmful radiation and disarming it," said Jack O'Malley-James, an astrobiologist at Cornell University in New York.
Working with exoplanet researcher Lisa Kaltenegger, also at Cornell, O'Malley-James recently modeled what a planet covered in biofluorescent life might look like. His results suggested that such a world could be spotted from Earth in the not-too-distant future.
The research, which was presented in April at the the Astrobiology Science Conference in Mesa, Arizona, is under review at The Astrophysical Journal; it can currently be found on the online pre-print website arXiv.
Fear the flare
Stars known as M-dwarfs make up the bulk of the stars in the Milky Way; some estimates put them as high as 75 percent of the stellar population. These long-lived stars are dim, so their planets must lie closer in than the Earth to keep water on the surface. Water is considered a key ingredient for the evolution of life as we know it, making planets capable of holding onto the life-giving liquid key targets for astronomers.
But sometimes these planets are too close for comfort. M-dwarfs can be extremely violent, spewing out flares of radiation that can strip away atmospheres and douse the surface of the world. In these cases, life might need a solar flare-screen.
"There are all sorts of ways life can protect itself” from radiation, O'Malley-James says. It could live underground or underwater, where rocks or oceans could shield it from the flares. But life under these circumstances would be impossible to spot using today's instruments.
After hearing about a species of coral that shifted light away out of the danger zone on Earth, O'Malley-James wondered if the same process might happen on other planets. If so, he surmised, it might allow Earthbound scientists to spot signs of life on worlds around M-dwarfs. That life doesn't have to be coral; it could be microbial, or a variety of other forms. The important part is that it is widespread enough to create a significant shift in the planet's color.
Then he and Kaltenegger went farther: they modeled what a planet covered in glowing life might look like from afar by simulating light from the coral on Earth. Because life would react to light from its star, the planet "wouldn't be constantly ‘on,’" O'Malley-James said. Instead, he anticipates that during periods of elevated ultraviolet light, such as during a flare, life would begin to glow faintly. Once the flare had washed over the planet, and the dangerous radiation no longer rained down, the glow would fade.
"We just imagined these planets that light up and advertise the fact that they're inhabited," he says.
Earth's friendly glow
There is precedent for known creatures using their glow powers this way. "Lots of things absorb light and emit it at other wavelengths," said David Gruber, a professor of biology and environmental science at the City University of New York who was not involved in the research. A marine biologist, Gruber frequently scuba dives among glowing marine creatures, and in 2015 discovered the first known biofluorescent sea turtle.
As O’Malley-James noted, these include certain species of coral that contain a special protein that absorbs sunlight and give off red, green and orange light. While Gruber said the function of biofluorescence in the coral remains debated, research has shown that it can function as a kind of sunscreen.
"As it absorbs ultraviolet light, it immediately converts that light into visible light," Gruber said. "Harmful ultraviolet light, instead of being absorbed by the skin and breaking bonds and causing mutations, is immediately shifted."
The coral is extremely efficient at converting the light. Virtually every photon that comes in is shifted. As Gruber puts it: "This stuff is bright." He points out that Australia's Great Barrier reef is large enough to be visible from space, though not its glow. Add in shallow water coral around the globe, and he wouldn't be completely surprised if astronomers spotted the glow from alien coral.
But they won't spot it anytime soon. O'Malley-James calculated that today's telescopes wouldn't be able to separate the faint glow from the bright star. However, the larger telescopes of the future, including several currently in the planning stages, might be able to. That's one reason the pair are studying the concept now, to provide insight into the technical requirements for such instruments.
Life isn't the only thing that glows. Several minerals redirect light from the sun, including calcite, agate and fluorite. Scientists can study the light from objects on Earth to determine if the glow they see is biological or not. When it comes to planets around other stars, however, determining if the light source is biological requires assuming life there evolved the same way it did on our planet, which may not be the case.
Still, a planet that changes color when hit by radiation could provide significant insight into what is happening at the surface, including potential life. "I like to dream that there are other worlds with these massive biofluorescing oceans that are waiting to be discovered," Gruber says.
Who could blame him?