The search for life beyond Earth is one of the most fascinating and challenging endeavors of modern astronomy. In the past few decades, thousands of exoplanets – planets orbiting other stars – have been discovered, some of them in the habitable zone of their host stars, where liquid water could exist on their surfaces. However, finding a habitable planet is not enough to confirm the presence of life. We also need to detect signs of biological activity in the planet’s atmosphere, such as oxygen, methane, or other molecules that could indicate living organisms.
To do this, astronomers need powerful telescopes that can directly image exoplanets and study their spectra – the light patterns that reveal the chemical composition of their atmospheres. Currently, only a few exoplanets have been directly imaged, mostly large and young gas giants that are still hot and bright from their formation. To image smaller and cooler rocky worlds, like Earth, we need the next generation of extremely large telescopes (ELTs) that are being built or planned around the world.
One of these ELTs is the European Extremely Large Telescope (ELT), which is expected to be operational by 2027. The ELT will have a primary mirror of 39 meters in diameter, making it the largest optical telescope ever built. The ELT will be equipped with two instruments that can directly image and analyze the atmospheres of exoplanets: the Mid-infrared ELT Imager and Spectrograph (METIS) and the High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI).
A recent study published in the Astronomical Journal simulated how these instruments could detect biosignatures on ten nearby rocky exoplanets, including Proxima Centauri b and GJ 887 b, two potentially habitable worlds around the closest stars to our Sun. The study found that the ELT could achieve a high enough signal-to-noise ratio to identify molecules such as oxygen, carbon dioxide, methane, and water vapor in the spectra of these planets, depending on their atmospheric properties and orbital configurations.
The study also compared the performance of the ELT with two other ELTs: the Thirty Meter Telescope (TMT) and the Giant Magellan Telescope (GMT), both planned to be operational in the 2030s. The study concluded that the ELT would have the best chance of detecting biosignatures on nearby rocky exoplanets in the next two decades, followed by the TMT and then the GMT.
The detection of biosignatures on exoplanets would not necessarily prove the existence of life, as some abiotic processes could also produce similar molecules. However, it would be a strong indication of possible biological activity and a major breakthrough in our quest for alien life. The ELT and other ELTs could open a new window into the diversity and complexity of life in the universe.