Researchers at Cornell University have made a remarkable breakthrough by creating the first map of colors produced by microorganisms that populate Earth's clouds. These tiny living beings, such as certain bacteria and algae, produce colored pigments to protect themselves from intense ultraviolet rays present at high altitudes. This unique color signature could now serve as a reference for detecting similar life forms in the atmospheres of other worlds.
The idea for this research came from astrobiologist Ligia Coelho, who noticed that the astronomical scientific community largely ignored the existence of these aerial ecosystems. She explains that these biological pigments are universal on Earth, produced by a wide variety of organisms to cope with difficult conditions. Their presence in clouds could therefore reveal active biological processes on distant planets.
Artist's representation of an Earth-like exoplanet with cloud cover hosting colorful life.
Credit: Adam B. Langeveld/Carl Sagan Institute. Adapted from NASA/Ames/JPL-Caltech. The team modeled how these color signatures would appear in exoplanet clouds. The results clearly show that clouds hosting microbial life would exhibit distinct spectral characteristics from those that don't contain any. This difference opens the way to a new detection method.
Next-generation telescopes, such as NASA's Habitable Worlds Observatory and the European Extremely Large Telescope, will be equipped to search for these color signatures. Lisa Kaltenegger, director of the Carl Sagan Institute, emphasizes that this approach completely transforms our perspective: what was once considered an obstacle could become an asset in the search for extraterrestrial life.
This discovery significantly expands the possibilities for detecting life in the Universe. Even on planets where the sky is constantly overcast, such as some potentially habitable super-Earths, astronomers could now look for biological clues in the very composition of clouds.
Spectroscopy and the Detection of Life
Spectroscopy is a technique that analyzes how matter interacts with light. Each substance, whether mineral or organic, absorbs and reflects light in a unique way, creating a kind of light fingerprint. This method is particularly useful in astronomy for studying the composition of celestial objects without having to approach them.
In the case of exoplanets, astronomers use spectroscopy to analyze light that passes through their atmosphere or is reflected from their surface. By breaking down this light into its different colors, they can identify the elements and compounds present. The presence of certain combinations of gases or particular spectral signatures can indicate biological activity.
The novelty brought by this research lies in the application of this technique to the clouds themselves. By establishing spectral models for terrestrial cloud microorganisms, researchers create a comparison basis for future observations. Telescopes will thus be able to search for similar signatures in the atmospheres of other planets.
This spectral method could detect life even under conditions where other approaches would fail. On planets whose surface is invisible due to permanent cloud cover, spectral analysis of clouds could reveal the presence of living organisms directly in the atmosphere, thereby significantly expanding the detection field of potentially habitable worlds.