Scientists at Cornell produced the first reflectance spectra for pigmented microbes that live in Earth’s clouds, creating a color-coded fingerprint that could reveal similar life in exoplanet atmospheres. Modeling shows clouds containing these biopigments would reflect light differently from sterile clouds, making the pigments a potential biosignature. The spectral library gives astronomers a target for future missions such as NASA’s Habitable Worlds Observatory and ESO’s Extremely Large Telescope. The team published their results in the Astrophysical Journal Letters on Nov. 11.
Could Alien Life Hide in Exoplanet Clouds? Cornell Maps a Microbial Spectral Fingerprint
Scientists at Cornell produced the first reflectance spectra for pigmented microbes that live in Earth’s clouds, creating a color-coded fingerprint that could reveal similar life in exoplanet atmospheres. Modeling shows clouds containing these biopigments would reflect light differently from sterile clouds, making the pigments a potential biosignature. The spectral library gives astronomers a target for future missions such as NASA’s Habitable Worlds Observatory and ESO’s Extremely Large Telescope. The team published their results in the Astrophysical Journal Letters on Nov. 11.
12:46 PM, 11/14/2025Science
Could color in clouds reveal life on other worlds?
Astronomers typically view clouds as a nuisance because they obscure observations, but new research from Cornell University suggests dense cloud layers might instead point the way to life on distant exoplanets.
Scientists at Cornell have produced the first reflectance spectra — a color-coded spectral fingerprint — for the vividly pigmented microorganisms that inhabit Earth’s clouds. These biopigments, produced by microbes to protect against ultraviolet radiation and other stresses, alter the way clouds reflect sunlight. That means clouds containing such organisms could exhibit measurably different reflectance signatures than sterile clouds.
How the study came about
The project was led by astrobiologist Ligia Coelho, a postdoctoral astronomy fellow at Cornell, with senior guidance from Lisa Kaltenegger, professor of astronomy and director of the Carl Sagan Institute. “We thought clouds would hide life from us, but surprisingly, they could help us find life,” Kaltenegger said.
“There is a vibrant community of microorganisms in our atmosphere that produces colorful biopigments, which have fascinated biologists for years. I thought astronomers should know about them,” said Ligia Coelho.
Biopigments are widespread across Earth’s biosphere — appearing in bacteria, archaea, algae, plants and animals — and serve protective roles against radiation, desiccation and resource scarcity. In the high atmosphere, cloud-dwelling microbes generate pigments specifically to shield themselves from abundant ultraviolet radiation.
Coelho and her collaborators converted laboratory and field pigment measurements into reflectance spectra, then ran those spectra through atmospheric and observational models. The results suggest that clouds populated by colorful microorganisms would produce distinct spectral features that could act as a potential biosignature when observed remotely.
What this means for exoplanet searches
While it remains unknown whether comparable airborne microbes exist beyond Earth, the new spectral library gives astronomers a concrete target. Next-generation observatories — including NASA’s Habitable Worlds Observatory and the European Southern Observatory’s Extremely Large Telescope (ELT) — could search for these pigment signatures in the atmospheres of temperate exoplanets.
The team’s findings were published in the Astrophysical Journal Letters on Nov. 11. The work opens a fresh pathway to detect life remotely: even cloudy skies might conceal detectable signs of biology.