Cloud microbes’ colours could help us detect life on other planets

The Importance of Microbes in Earth’s Atmosphere

The colors of microbes living in high-altitude clouds have been analyzed for the first time, providing valuable insights that could aid in the search for extraterrestrial life. These microscopic organisms, found in Earth’s atmosphere at concentrations of up to 100,000 microbes per cubic meter, play a significant role in cloud formation and survival in extreme conditions.

One fascinating aspect of these airborne microorganisms is their production of pigments to shield themselves from the harsh ultraviolet light at such heights. These biopigments serve as universal biosignatures that could potentially be used to identify similar life forms on other planets by studying the reflected spectra of light.

Research conducted by Ligia Coelho at Cornell University involved culturing microbes collected from Earth’s atmosphere by Brent Christner and his team at the University of Florida. By measuring the reflectance spectra of the pigmented compounds produced by these microbes, Coelho’s team discovered a range of vibrant colors including yellow, orange, and pink, attributed to carotenoid pigments such as beta-carotene.

Furthermore, simulations conducted by the team demonstrated how these spectra would vary under different environmental conditions, offering a basis for detecting life in clouds beyond Earth.

Implications for Exoplanet Exploration

Astronomers are actively searching for signs of life on exoplanets by analyzing reflected light for chemical signatures and surface features that could indicate the presence of living organisms. While clouds have traditionally posed challenges in this pursuit, the study suggests that high concentrations of pigmented microorganisms in a planet’s atmosphere could alter its spectra in a detectable manner.

Future space telescopes like NASA’s proposed Habitable Worlds Observatory hold promise for enhancing our ability to detect life in distant star systems. However, the detection of airborne microbes from such vast distances would require exceptionally high concentrations, surpassing current detection thresholds.

Clare Fletcher from the University of New South Wales emphasizes the importance of searching for carotenoids produced by stratospheric microbes alongside chlorophyll from plants as potential indicators of life on exoplanets. However, Peter Tuthill from the University of Sydney remains skeptical about the practicality of identifying stratospheric biosignatures in the search for extraterrestrial life.