Scathing Report Claims Energy Megaproject Will Ruin ‘Best Place on Earth for Astronomy’

A new report by the European Southern Observatory says a planned industrial megaproject will significantly brighten the skies in Chile’s Atacama Desert, jeopardizing some of the best conditions in the world for ground-based astronomy.

The project would specifically affect the Paranal Observatory, which hosts ESO’s Very Large Telescope (VLT) and Cherenkov Telescope Array Observatory (CTAO-South). The report stresses that light pollution at the respective telescopes would increase by at least 35% and more than 50%, hindering scientists’ abilities to observe and understand the universe. The technical summary of the team’s report can be read here.

CTAO-South is currently under construction, as is ESO’s Extremely Large Telescope (ELT), the successor to VLT, the site of which was chosen about 15 miles (25 kilometers) from Paranal 15 years ago.

The proposed industrial complex is called INNA, short for Proyecto Integrado de Infraestructura Energética para la Generación de Hidrógeno y Amoníaco Verde.

Light pollution is a major threat to ground-based observatories—not just amateur astronomers in their backyards, but also large, heavily invested and multinational observatories. In 2023, data from NOIRLab’s Globe at Night project revealed that the night sky got 9.6% brighter each year from 2011 to 2022, on average, indicating that a “location with 250 visible stars would see that number reduce to 100 visible stars over the same period,” according to the affiliated study published in Science.

“With a brighter sky, we severely limit our ability to directly detect Earth-like exoplanets, observe faint galaxies, and even monitor asteroids that could cause damage to our planet,” said Itziar de Gregorio-Monsalvo, ESO’s Representative in Chile, in an observatory release. “We build the largest and most powerful telescopes, in the best place on Earth for astronomy, to enable astronomers worldwide to see what no one has ever seen before. Light pollution from projects like INNA doesn’t just hinder research, it steals our shared view of the Universe.”

The graph below shows how dark Paranal’s skies are relative to the observing conditions of other famous observatories.

According to the report, the INNA project could impact the night sky with artificial light contamination, increase ground vibrations due to the installation of wind turbines, increase atmospheric turbulence due to the operation of those same wind turbines, and contaminate optical surfaces—including telescope mirrors and lenses—with dust.

“A 1% artificial light contamination means that above every 100 photons from the natural sky brightness, there is 1 on average which comes from light pollution, which cannot be distinguished by another photon coming from a faint object at the edge of the Universe as detected by the most powerful telescope ever built—like the ELT,” stated the report. “Every photon counts in astronomical research.”

“Detailed analyses … show that the INNA project executed at the currently baselined site will significantly and negatively impact the performance of all ESO’s telescopes at the site, in a way that due to the proximity, could not be mitigated,” the report concluded. It stated that the limits of ground vibration on the VLT interferometer and the ELT itself would likely be exceeded by the project, and the wind turbines would produce similar turbulence in the air to that of wind farms, inhibiting the observatory’s ability to see the skies.

“Taken together, these disturbances seriously threaten the current and long-term viability of Paranal as a world-leader in astronomy, causing the loss of key discoveries about the Universe and compromising Chile’s strategic advantage in this area,” de Gregorio-Monsalvo added. “The only way to save Paranal’s pristine skies and protect astronomy for future generations is to relocate the INNA complex.”

The report assumed clear skies, though Martin Aubé, an expert on sky brightness, said that light pollution from an entity like INNA would be exacerbated by cirrus cloud cover, which is thin enough not to disrupt ordinary astronomical observations, but which would reflect artificial light, worsening the problem.

“Should the INNA project be approved, the value of the telescopes installed or planned by ESO would be substantially decreased,” the report concluded. “These losses are manyfold and not recoverable world-wide.”

To be clear, ESO authorities are not up in arms about the INNA project in itself. The proximity is the problem.

“For us Chile should not have to make a choice between hosting the most powerful astronomical observatories and developing green-energy projects,” said the observatory’s director general Xavier Barcons, in the same release. “Both are declared strategic priorities by the country and are fully compatible—if the different facilities are located at sufficient distances from one another.”

A full technical report on the potential impacts of INNA on Paranal will be submitted to authorities this month, and made public before April 3. Hopefully the parties can come to a mutually beneficial decision—one that doesn’t put ambitions of clean energy projects at odds with astronomical observations.