The European Southern Observatory (ESO) is constructing what will be the world’s largest optical telescope in Chile’s Atacama Desert, a region renowned for having some of the darkest skies on Earth.
Located at the Paranal Observatory site, the Extremely Large Telescope (ELT) project represents a major advancement in ground-based astronomy. The facility is being built on Cerro Armazones, near the existing Very Large Telescope array, and aims to transform scientific understanding of the universe.
The Atacama Desert’s unique conditions—including its extreme dryness, high elevation, and minimal light pollution—provide over 300 clear nights annually, making it ideal for deep-space observation. These factors have enabled significant discoveries, such as the first direct image of an exoplanet and research confirming the accelerated expansion of the universe, which contributed to a Nobel Prize in Physics in 2020.
However, the pristine dark skies critical to these observations are facing potential threats. In December 2024, AES Andes, a subsidiary of the U.S.-based AES Corporation, submitted an environmental impact assessment for a large industrial complex named Inna. The proposed project would be situated between 5 and 11 kilometers from the Paranal telescopes.
Astronomers and environmental experts warn that the development could cause irreversible damage to astronomical observations due to light pollution during the complex’s operational lifetime. The proximity risks degrading the quality of data collected by both current and future instruments at the site.
Following widespread concern from the scientific community—including astronomers, physicists, and Nobel laureates—the company withdrew the project in January 2025. Despite this, the incident has prompted ongoing reviews of environmental regulations governing astronomical zones in Chile, with officials noting that current rules may be inadequate or outdated.
ESO emphasizes that Paranal remains a vital asset for global astronomy, having contributed to landmark breakthroughs since its opening in 1999. The observatory continues to support international research efforts, including those involving Chile’s growing astronomical community.
Preserving the natural darkness of the Atacama sky is seen as essential not only for ongoing scientific operate but likewise for protecting one of Earth’s last truly pristine views of the cosmos for future generations.
