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The European Southern Observatory is at serious risk of losing the clear skies above its Paranal Observatory in Chile’s Atacama Desert, officials said, due to a proposed industrial complex put forward by the subsidiary of a U.S. power company.
Paranal Observatory is home to ESO’s Very Large Telescope (VLT), which comprises four telescopes each with a 27-foot (8.2-meter) mirror and four auxiliary telescopes with 6-foot (1.8-meter) mirrors. Working together, the telescopes produce some of the sharpest views of the universe. Observatory officials are seriously concerned that the proposed industrial project will go ahead, diminishing what Paranal can see and permanently changing nighttime visibility in some of the best skies for astronomical research.
Right next door
The project, dubbed Inna, is a proposed industrial-scale green hydrogen project. The project’s total footprint would cover more than 7,413 acres of the Atacama and would include a port, ammonia and hydrogen production plants, and thousands of electric generators.
All of this would need to be built from the ground up, with the proposed project site located 3 to 7 miles (5 to 11 kilometers) from Paranal’s telescopes. The company, AES Andes, submitted an Environmental Impact Assessment for the project to Chilean authorities late last month.
“As with any project, our partnership with local communities and stakeholders is a top priority, ensuring we are supporting local economic development, while maintaining the highest environmental and safety standards,” said Javier Dib, AES’ Chile Market Business Leader, in a company statement announcing the submission.
Well, the environmental impacts are precisely what the European Southern Observatory officials are concerned about. The Atacama Desert has some of the darkest, clearest skies of anywhere on Earth. There is little moisture in the air, minimizing the amount of light absorbed by water in the atmosphere, and it’s at high elevation, reducing the amount of wobble that Earth-based astronomers typically have to contend with when imaging distant sources through the atmosphere.
Paranal’s unique location and impact
From its perch in Chile’s Atacama, the Very Large Telescope has captured ancient and recent astronomical events alike, both in our galaxy and far beyond its reaches. In 2021, the telescope snapped images of 42 of the solar system’s biggest asteroids. It continued the space rock trend in 2023, when two teams revealed the telescope’s images of the aftermath of NASA’s DART mission, which tested the viability of altering a natural body’s orbit in space. The same year, the telescope spotted gas clouds that may have formed in the aftermath of the first stars and, just two months ago, a different team used the telescope to capture the first detailed image of a star outside our galaxy.
Because of the Atacama’s natural disposition for astronomy, it is home to many current and planned telescopes, including Paranal, the Rubin Observatory (which hosts the world’s largest digital camera), and the under-construction Giant Magellan Telescope at the Las Campanas Observatory. The LSST Camera at the Rubin Observatory is set to have its first light later this year—something to look forward to in a year crammed with astronomical events.
“Chile, and in particular Paranal, is a truly special place for astronomy—its dark skies are a natural heritage that transcends its borders and benefits all humanity,” said Itziar de Gregorio, ESO’s Representative in Chile, in an observatory release. “It is crucial to consider alternative locations for this megaproject that do not endanger one of the world’s most important astronomical treasures.”
In 2022, a team of researchers found that light pollution over Paranal was substantially less than that over 27 other major observatories. That research found that two-thirds of all large observatories the team studied already had light pollution increase by 10% over assumed natural levels, suggesting that light pollution is taking a serious toll on astronomical observations already.
A graph illustrating how dark skies are above Paranal compared to other observatories. Graphic: Falchi et al. 2023 “The outcomes emerging from this work are sending what might be the last call for a serious, collective, unambiguous, no-compromise action to lower light pollution now, whether it is generated from artificial light or from sunlight reflected by artificial objects in orbit,” the team wrote. “Failing to take action implies a progressive decline of our ability to explore our Universe.”
Astronomy under threat
“The proximity of the AES Andes industrial megaproject to Paranal poses a critical risk to the most pristine night skies on the planet,” said ESO’s Director General, Xavier Barcons, in the observatory release. “Dust emissions during construction, increased atmospheric turbulence, and especially light pollution will irreparably impact the capabilities for astronomical observation, which have thus far attracted multi-billion-Euro investments by the governments of the ESO Member States.”
Infrastructure on the ground is not astronomers’ only concern. Earth orbit is cluttered with satellites which complicate imaging of the night sky. Megaconstellations including SpaceX’s Starlink create streaks on astronomical images as the individual spacecraft transit the night sky. Such satellite swarms even vex space-based telescopes, as seen in some Hubble Space Telescope images. There are tricks to cleaning astronomical images of these streaks, but they are nevertheless a problem.
Light pollution is getting worse, according to recent research. In 2023, a group of researchers reviewed over 50,000 observations made around the world between 2011 and 2022 as part of NOIRLab’s Globe at Night project. The researchers found that the night sky became 9.6% brighter each year, causing some dimmer stars to completely disappear in the sky for some stargazers.
Photo: Lam Yik Fei (Getty Images) Light pollution’s impact on the Atacama and astronomy
Eventually, the Very Large Telescope will be succeeded by the Extremely Large Telescope (inventive names, I know), which will be 128 feet (39 meters) across and is set to become the largest visible and infrared light telescope in the world. The Extremely Large Telescope will collect 100 million times as much light as the human eye and will reveal details of distant exoplanets, black holes, the evolution of galaxies, and the universe’s earliest days. The telescope will be sited near the VLT, at Cerro Armazones, and its first light is now expected for 2028—though the ESO’s website offers a more cautious “the end of this decade.”
“Astronomical observatories can be seen as the proverbial canary in a coal mine,” wrote the team that evaluated the relative darkness of observatories’ skies in its 2022 paper. “If we are not able even to keep the canary alive, then we can forget being able to solve the problem of light pollution as a global environmental issue.” Furthermore, the group noted, other negative consequences of light pollution will persist, including the disruption of circadian rhythms and other negative health consequences in Earth’s biodiversity.
In its release, the ESO advocated for the relocation of the AES Andes project, stating that moving the industrial complex “remains the only effective way to prevent irreversible damage to Paranal’s unique skies.” Meanwhile, the company awaits word from Chilean authorities on whether the project’s environmental impact is minimal enough to proceed as proposed.
A cornerstone of the company’s messaging is decarbonizing its energy matrix and increasing the amount of energy sourced from renewable sources. There would be painful irony in Chilean authorities allowing a green energy project to proceed at the expense of clear skies for astronomers.
