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A new industrial megaproject threatens the view of the world's best observatories

Astronomers have been battling threats to their clear skies on all fronts lately. One of the most notable battles, which we have reported on repeatedly, is the one against Starlink and other mega-constellations of satellites, which, while they offer high-speed internet in the most far-flung places, also disrupt observations by sensitive telescopes due to their reflectivity and fast movement speed.

They also pose a global problem, whereas a more down-to-earth issue is cropping up at one very special observatory. A vast industrial plant threatens the European Southern Observatory's Paranal telescope planned only a few kilometers from the site.

The ESO recently released a statement calling on the government of Chile, where Paranal is located, to consider moving the project elsewhere. Currently, AES Andes, a subsidiary of AES Corporation, an American power utility, recently submitted a proposal for an environmental review of a 3,000-hectare industrial area that includes hydrogen and ammonium factories, electricity-generating machinery, and, importantly, a lot of lights.

Lights are part and parcel of any large industrial project, but they pose a particular threat to Paranal. In a recent study, it was found to be the observational site with the least amount of light pollution. Any significant increase to that baseline over only about 0.1% of the generic background level could have a massive negative impact on the capabilities of the telescope located there.

That telescope has been an essential part of the astronomical community and contributed to research such as the Nobel Prize-winning 2020 studies into the Sgr A*, the supermassive black hole at the center of our galaxy. It also represents billions of dollars of investment from the European Southern Observatory member states.

When thinking about natural resources, a clear sky might not come to someone's mind, but it certainly is for Chile. In addition to Paranal, two other Chilean observatories are in the top three least light-polluted major astronomical observatories—Armazones and Tokyo Atacama. It also has four more in the top 15, making it one of the best contributors in the world to this type of astronomy.

That contribution is planned to grow with the ESO's ongoing development of the Extremely Large Telescope not far from the Paranal site. While the light pollution from the planned industrial facility might not reach as far as what will be the biggest telescope of its kind in the world, any precedent by the Chilean government to approve projects that would undercut investment by ESO and other astronomical bodies would be detrimental to the long-term outlook of observations in the country.

Since the AES Andes proposal is still in the environmental impact assessment phase, it's still early enough to provide feedback for a potential alternative. ESO's letter shows support for the project in concept but suggests moving it to a different location so as not to negatively affect the telescope. Whether or not that is feasible and whether or not the Chilean government will support it at all remains to be seen. But this threat to one of the world's great observatories shouldn't be ignored.