In Chile’s northern Atacama Desert, the pristine dark skies above the world’s largest telescopes are under threat from a proposed green energy project that would be built just a few kilometers away, the European Southern Observatory (ESO) said today. The planned complex includes a nearby port and photovoltaic solar arrays and wind turbines that would power the production of ammonia and “green” hydrogen. Even with the best designed lighting, it would fill the sky with stray light, says ESO Director Xavier Barcons. Among the vulnerable instruments is the Extremely Large Telescope (ELT), which has a record-setting 39-meter-wide mirror and will be completed by the end of the decade.
The Atacama proposal comes from a subsidiary of the U.S. energy company AES Corporation. After AES revealed the project in August 2024, Barcons says ESO met with the company several times between September and December, explaining the threat the city-size complex would pose to the observatories. Nevertheless, in late December AES submitted the proposal to Chile’s Environmental Assessment Service for an impact assessment. A press release from the company does not mention a start date for the project and says no decision on investment has been made yet.
“This is a real threat to what we have already done there, but very importantly to the future of the observatories in Chile,” Barcons says. Putting the planned energy project so close to astronomical facilities “would be really a stupid idea,” says astronomer Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics, who uses ESO’s Very Large Telescope (VLT)—currently the world’s largest optical telescope—to study the area around the Milky Way’s central supermassive black hole, Sagittarius A*.
ESO chose the summit of Cerro Paranal in Chile’s northern Atacama Desert as the site of the VLT because of its extremely dry air and low levels of light pollution—lower than at any other major observatory site around the world. Operating since 1998, the VLT, which comprises four individual scopes each with 8.2-meter mirrors, carried out studies of Sagittarius A* that contributed to the 2020 Nobel Prize in Physics, confirmed the accelerating expansion of the universe, and took the first direct image of a planet around another star.
The ELT is taking shape on nearby Cerro Armazones, and ESO is also a partner in the Cherenkov Telescope Array, a gamma ray observatory, which is beginning construction nearby. Together, the three facilities occupy a triangular territory 25 kilometers across that by Chilean law is spared from development to protect their viewing. The 16 European member states of ESO have invested several billion euros in the facilities.
The AES project would occupy several sites totaling 3000 hectares, and the plants making hydrogen and ammonia with renewable energy would be sited just 5 kilometers from the VLT. Construction of the complex will create dust, a threat to delicate optics, but that would be manageable and temporary, Barcons says. More worrying is the permanent loss of the area’s remarkable dark skies. ESO has been using light pollution models developed by researchers in Canada to estimate the impact of AES’s plans. “Even if [AES] do a perfect job, using perfect lights that probably don’t even exist and perfect shielding, there will be an impact and that will be significant,” Barcons says.
Astronomer Francesco Pepe of the University of Geneva, a member of the ESO Council who is principal investigator for the ESPRESSO spectrograph on the VLT, says the effects on most exoplanet studies, one of his specialties, will be modest because observers detect and study the planets by looking at their impact on relatively bright stars. But the harm will be greater for researchers trying to capture the much dimmer light reflected from an exoplanet itself. And studies of the distant, early universe will suffer even more. “In general, a bright [polluted] sky will impact the more distant universe because the distant objects are fainter,” Pepe says.
ESO has argued that other sites in the sparsely populated Antofagasta region would be equally suitable for the project, and that relocating it 50 kilometers from the observatories would minimize the harm. “We’re very supportive of sustainability,” Barcons says. But, he adds, “Paranal and Armazones are the darkest places in the world for optical and infrared observations. There’s no reason to challenge that to produce green hydrogen.”
ESO “tried to have an open discussion” with AES, Pepe says. “They did not do the same, they did not take into account other interests.”
A spokesperson for the company defended the project in a statement sent to ScienceInsider: “The INNA project will be located in an area that the State of Chile has defined for the development of renewable energies... and specifically incorporates in its design the highest standards in terms of lighting.” The statement added: “We understand the concerns raised by ESO … and are are committed to collaborating with all interested parties in the environmental processing process.”
There are “geopolitical and national strategic interests” at play, Pepe says. “There seems to be some tension within the Chilean government between the ministers of energy and so on, on one side, and the ministers of science on the other side. … What is a real shame here is that probably with a more open discussion, this situation could have been avoided.”
The Chilean government has been making a push to encourage renewable energy. In 2023, it published a green hydrogen action plan that calls for using the country’s abundant wind and solar energy to make hydrogen for domestic use and export. Such projects often split local communities, some welcoming the jobs and infrastructure, others concerned about the environmental impact, says Bernardita Ried Guachalla, a Chilean astronomer working at the SLAC National Accelerator Laboratory. “Finding an equilibrium is not easy,” she says.
From California, Guachalla is working to raise the alarm about this new threat to astronomy in her country. “It’s difficult,” she says. “It’s a really, really big company and they have a lot of power. It’s not easy to fight someone that has a lot of power.”
Update, 10 January, 6:45 p.m.: This story has been updated with a comment from AES.