Clouds may seem like a barrier when looking for life on distant planets, but new research shows they could actually be the key.
Scientists at Cornell University have discovered that clouds—thick, bright, and often mysterious—might help reveal whether an exoplanet hosts life.
Astrobiologist Ligia Coelho, a postdoctoral fellow at Cornell’s Carl Sagan Institute, led a study that created the first-ever “color key” for microorganisms living in Earth’s atmosphere.
These microbes, though rare, produce colorful pigments that help them survive harsh conditions high above the ground.
The study, “Colors of Life in the Clouds,” was published in The Astrophysical Journal Letters.
On Earth, these tiny life forms aren’t numerous enough to be seen from space. But by studying how they reflect light, Coelho and her team built a reference map—called a reflectance spectrum—that astronomers can now use when observing exoplanets.
This means that even if a distant planet is covered in thick clouds, astronomers might still detect hints of life hidden within them.
“There is a vibrant community of microorganisms in our atmosphere that produce colorful biopigments,” Coelho said. “I thought astronomers should know about them.”
Coelho collected seven species of these airborne microbes with help from collaborators at the University of Florida, who used a high-altitude balloon to capture samples from the stratosphere, about 21 to 29 kilometers above Earth. She then grew the bacteria in Cornell’s labs and measured how they reflected light of different wavelengths. Each microbe’s color signature reveals information about its environment—its pigments protect it from ultraviolet radiation, dryness, and extreme temperatures.
According to Lisa Kaltenegger, director of the Carl Sagan Institute and co-author of the study, this discovery opens an unexpected door. “We thought clouds would hide life from us, but surprisingly, they could help us find it,” she said. With this new data, scientists can search for colorful biosignatures even on exoplanets with complete cloud cover.
Modeling results from the study show that a planet with clouds full of pigmented microbes would look very different from one without them. To be detectable, these bacteria would need to exist in large numbers and thrive in humid, cloud-filled worlds. Future space missions such as NASA’s upcoming Habitable Worlds Observatory and Europe’s Extremely Large Telescope will be powerful enough to test this idea in the coming decades.
“Biopigments are universal,” Coelho said. “They help life survive radiation, dryness, and other stresses. Now we have a new way to look for them—through the clouds of distant worlds. If life looks like this, we finally have the tools to recognize it.”
Source: Cornell University.
