A high-stakes face-off is brewing in the arid deserts of northern Chile, between astronomers building the world’s largest optical telescope and a proposed green energy megaproject from an international corporation that threatens those plans.
For decades, astronomers have prized Chile’s Atacama Desert as a premiere location for studying the universe. Sparsely populated, far from sources of terrestrial light pollution and high above most starlight-scattering clouds and atmospheric turbulence, the Atacama has sprouted multiple world-class observatories to take advantage of what are thought to be Earth’s darkest and clearest night skies. Chief among these is Paranal Observatory, built and operated by the European Southern Observatory (ESO) consortium. Paranal’s facilities, however, should soon be outclassed by ESO’s under-construction $1.5-billion Extremely Large Telescope, or ELT, which boasts a light-gathering primary mirror nearly 40 meters in diameter—unless, that is, disruptions from another nearby construction project spoil the overhead view.
Backed by AES Andes, an offshoot of The AES Corporation, an American company, the $10-billion INNA (Integrated Energy Infrastructure Project for the Generation of Hydrogen and Green Ammonia) project includes plans for multiple sites across more than 3,000 hectares (about 7,400 acres). As proposed, parts of the sprawling INNA complex could encroach as close as five kilometers to Paranal and its telescopes, causing effects so devastating that to mitigate them could require relocating the energy project 10 times farther away, ESO officials say.
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“Dust emissions during construction, increased atmospheric turbulence and especially light pollution will irreparably impact the capabilities for [regional] astronomical observation,” said ESO director general Xavier Barcons in a press release calling for INNA’s relocation. The proximity of the AES Andes industrial megaproject to Paranal “poses a critical risk to the most pristine night skies on the planet.”
The Best Skies on Earth
ESO has abundant evidence to back the “most pristine night skies” claim. As it noted in its press release, a 2023 study led by light pollution researcher Fabio Falchi, then a doctoral student at the University of Santiago de Compostela in Spain, found that of the 28 major observatories across the globe, Paranal was the darkest site of all. The site where the ELT is currently being constructed, Cerro Armazones, is a close second. Importantly, these sites are two of only six shown to possess skies with a less than 1 percent increase in sky brightness from estimated preindustrial levels. Most other major observatories—nearly two thirds of those considered in the study and all that are within the continental U.S.—now face compromised observations because their skies have been made far brighter by light pollution, Falchi’s study reported.
Because of Chile’s near-ideal conditions for astronomy, it has become home to almost 40 percent of the world’s ground-based astronomy observing capacity. Including current projects under construction, within the next decade that number will increase to 60 percent. The scientific bounty from this trend has already been revolutionary, and telescopes gazing deep into the Atacama’s superlatively dark skies have played a role in numerous major discoveries—such as what may be the first images of an exoplanet and, separately, of the Milky Way’s central supermassive black hole. The ELT and other next-generation telescopes there are poised to deliver even more extraordinary advances, possibly including breakthrough new measurements of dark energy and the first-ever direct images of rocky, Earthlike exoplanets.
This makes any threat to the natural celestial purity of this remote region of Chile a threat to the present and future of ground-based astronomy as a whole. If the INNA project proceeds as planned, “there will be corners and edges of the exploration of the universe that will not be accessible anymore,” Barcons says. And many of these areas are precisely those the ELT and other in-development giant telescopes were designed to probe, he adds.
A Megaproject in Micro Detail
AES conceived and designed the INNA project in response to Chile’s National Green Hydrogen Strategy, a plan of action for making the nation a global front-runner in renewable energy production. That blueprint also declared several Chilean sites as renewable energy hubs; the complex would be located within one of them. Besides the project’s main facility, a hydrogen and ammonia production plant, INNA’s plan also calls for building thousands of solar and wind power generators, as well as a coastal port and desalination site, all connected to massive energy storage systems via snaking pipelines and transmission wires.
In a statement to Scientific American, AES Andes officials noted that “our partnership with stakeholders is a top priority, ensuring we are supporting local economic development while maintaining the highest environmental and safety standards. We understand there are concerns raised by ESO regarding the development of renewable energy projects in the area and are committed to collaborating with all stakeholders throughout the environmental permitting process.”
The project has been designed to comply with recently expanded regulatory requirements from the Chilean Ministry of the Environment on light pollution passed in 2022, which limit artificial light pollution in designated “astronomical areas” to a 10 percent increase over natural levels and set a 1 percent light pollution limit for individual sites. Notably, although an individual facility may comply with the 1 percent limit, the cumulative amount of light pollution in an astronomical area is permitted to reach a level of 10 percent. And that higher level of light pollution is exactly what ESO officials fear INNA will reach, with catastrophic implications for Paranal and the ELT.
Dark Disagreements
AES Andes contests such dire appraisals, noting in its statement that both Paranal and the ELT are “outside the significant [light pollution] impact area calculated for the project,” at “19.6 and 29 km away” from INNA, respectively. The ESO press release, however, stated that at least one of the project’s facilities will be between 5 and 11 km from the Paranal telescopes.
Additionally, AES Andes said in its statement that the sky brightness at the telescope sites will only increase by 0.09 percent at the ELT and 0.27 percent at the Very Large Telescope, also located in the Atacama Desert. But according to a report from Chile’s Ministry of Foreign Affairs, ESO has said that the light pollution data provided by AES are based on Project Terra, an older and much smaller version of INNA. According to the report, the AES Andes team communicated to ESO that the INNA project could produce up to five times more power compared with the older version. Using this estimate in its analysis, ESO found that the majority of the observing region for Paranal’s telescopes would see a 5 to 10 percent increase in background light from the INNA project, including an at least 3 percent increase in brightness for the darkest observable part of the sky.
Although seemingly small, such increases would significantly decrease the capabilities of affected telescopes, both big and small. A small increase in sky brightness makes the sky background noisier, which then requires astronomers to observe a faint object for much longer in order to get a clear signal. This not only gives the telescopes less time to observe more objects but also makes very faint objects such as very early galaxies and potentially habitable exoplanets impossible to see at all; if the object is faint enough, the image will become saturated before the signal becomes clear. “Having brighter sky means that your opportunity is shrinking. It is like you’re having a smaller telescope,” Falchi says, which renders a large project like the ELT “a waste of money and resources.”
Barcons says that ESO privately presented its concerns to AES in December of last year but that the company submitted an unchanged assessment to the Environmental Impact Assessment System (SEIA), run by Chile’s Environmental Assessment Service, just a few days later. “They already announced to us that they were not going to change it,” he says.
A Bright Future?
Both ESO and the Chilean Astronomical Society (SOCHIAS) emphasize that they do not want the project to be canceled altogether. Instead both groups are asking that INNA be moved at least 50 km away from the observatories. Chiara Mazzucchelli, president of SOCHIAS, believes that both projects can coexist. “Chile has the capacity to be a worldwide leader in both green energy and in astronomy,” she says. But so far, AES Andes’s sole response to relocation requests has been to note that INNA is within a designated renewable energy hub as defined by Chile and that it “[trusts] in the robustness of Chile’s Environmental Impact Assessment System,” Mazzucchelli says.
Coexistence is the way forward, says Bernardita Ried Guachalla, a Chilean doctoral candidate at Stanford University. There’s much to gain from developing green energy, but that shouldn’t come at the cost of Chilean astrophysics, which has benefited immensely from partnerships with global research institutions seeking time on the nation’s crop of telescopes. “From the science perspective, [Chile wins] a lot,” she says, noting that the nation’s astronomers now have access to “the best laboratories in the world.” Indeed, over the past couple of decades, the number of astronomy Ph.D. students has increased from five in 1990 to 40 in 2005, and Chile has risen to 12th place globally in astronomy paper citations per year, a striking number considering its size and gross domestic product. Outside of astronomy, hosting Earth’s greatest ground-based telescopes also brings engineering careers, astronomy tourism, and greater international investment and prestige.
As part of the SEIA approval process, the INNA project must now undergo a period of review in which public commentary is collected. SOCHIAS, ESO and leading local Chilean astronomers are encouraging members of the community, both in and outside of astronomy, to speak up on behalf of the observatories.
“The point is that this is no random place for us, for astronomy,” Barcons says. “It’s unique. There’s nothing better on Earth, and we’re putting the biggest telescope in there. So that will be gone forever if they do this.”
Organizers and citizens have until the beginning of April to give feedback to SEIA on the project. After that, the project’s future—and perhaps with it, the future of global ground-based astronomy—will be decided.
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