The Extremely Large Telescope (ELT) is set to transform our understanding of nearby star systems, with the potential to detect signs of life on exoplanets orbiting Proxima Centauri, the closest star to the Sun, in under half a day. A recent simulation study by Miles H. Currie and Victoria S. Meadows outlines how the ELT's immense light-gathering power and unmatched resolution could enable astronomers to differentiate between living and lifeless planets using only the reflected light from their atmospheres. This groundbreaking possibility is detailed in a 2025 study, which models the telescope's capability to extract molecular fingerprints from exoplanets that do not transit their host stars. Their findings, available on arXiv, suggest that the answer to one of astronomy's most profound questions—are we alone?—may soon be within reach.
Situated high in the Atacama Desert of Chile, the ELT is expected to commence operations in 2028. With a primary mirror measuring an astonishing 39 meters, it will be the largest optical/infrared telescope ever constructed on Earth. This vast surface area will enable the ELT to collect more light than any previous ground-based telescope, producing images that are up to 16 times sharper than those captured by the Hubble Space Telescope.
While other telescopes, such as the James Webb Space Telescope (JWST), have made significant strides in analyzing exoplanet atmospheres during planetary transits, they encounter limitations. Many exoplanets, particularly promising Earth-like candidates, do not transit from our line of sight. This is where the ELT revolutionizes the field. Instead of waiting for a planet to cross in front of its star, the ELT will capture reflected starlight directly from the atmospheres of exoplanets.
Utilizing cutting-edge high-contrast imaging and spectroscopy, the ELT can isolate molecular signatures, including oxygen, carbon dioxide, and water vapor—crucial markers that may indicate biological activity. To assess the ELT's potential, Currie and Meadows conducted comprehensive simulations of four Earth-like worlds orbiting nearby red dwarf stars:
A lush, non-industrial Earth rich in water and plant life An ancient Archean Earth with primitive life and minimal oxygen A desiccated, oceanless world resembling Venus or Mars A barren, prebiotic Earth with the chemical potential for life but devoid of organismsThe researchers also examined Neptune-sized exoplanets for comparison, anticipating that their thick atmospheres would produce distinct spectral patterns. Their objective was to ascertain whether the ELT could reliably differentiate between living and lifeless planets while minimizing false positives and negatives.
Their conclusion was unequivocal: with just ten hours of observation, the ELT could likely identify atmospheric biosignatures on an Earth-like planet orbiting Proxima Centauri. For gas giants, significant spectra could be obtained in as little as one hour.
Located a mere 4.24 light-years away, Proxima Centauri hosts at least two known exoplanets: Proxima b and Proxima d. Although the habitability of Proxima b remains a topic of debate, its position within the star's habitable zone and proximity to Earth render it an ideal candidate for future observations. If a thin atmosphere exists around Proxima b, the ELT could potentially detect it. Should this atmosphere contain biological molecules, the implications for humanity would be monumental.
With the ELT's advanced capabilities, astronomers will not be confined to sporadic planetary alignments or indirect detection methods. They will have the opportunity to directly observe exoplanets, paving the way for a more thorough and continuous exploration of nearby planetary systems.
The study also emphasizes the importance of caution regarding spectral ambiguity. Not every detection of oxygen or methane should be interpreted as definitive evidence of life. Natural, abiotic processes can produce chemical signatures that mimic those of living organisms. Therefore, the ELT's resolution and sensitivity are paramount. By integrating multiple spectral features and high-resolution data, researchers aim to construct robust biosignature frameworks, reducing the probability of erroneous conclusions.
In this context, the ELT will not only be a tool for searching for life but will also play a crucial role in defining what constitutes credible evidence of biological activity on distant worlds.
