In January, the European Southern Observatory (ESO) publicly raised the alarm about the threat that the industrial megaproject INNA posed to the world’s darkest and clearest skies for astronomy, those of ESO’s Paranal Observatory and the site of the CTAO’s southern hemisphere array (CTAO-South). The project — by AES Andes, a subsidiary of the U.S. power company AES Corporation — includes multiple energy and processing facilities, spread over an area of more than 3,000 hectares, the size of a small city. Its planned location is just a few kilometers from the Paranal telescopes. A preliminary analysis revealed that, due to its size and proximity to Paranal, the INNA project posed significant risks to astronomical observations. Now, an in-depth technical analysis by ESO has confirmed that INNA’s impact on the facilities at Paranal Observatory, Chile would be devastating and irreversible.
ESO’s technical report focuses on those site characteristics that are most critical for the performance of the observatories and that could be impacted by the INNA project, concluding that the construction and operation of this project will cause artificial light contamination (“light pollution”) and an increase in ground motions or vibrations, atmospheric turbulence and dust contamination of optical surfaces.
“ESO has done an outstanding job in conducting this thorough technical analysis, providing valuable insights into the potential impacts of the planned INNA project,” says Stuart McMuldroch, CTAO ERIC Director General. “The findings are very concerning, and we support their efforts to achieve a relocation of the planned facility.”
According to ESO’s analysis, the industrial complex would increase light pollution above the Very Large Telescope (VLT), which is about 11km from the planned INNA location, by at least 35% above the current artificial-light baseline levels. Another of the Paranal facilities, ESO’s Extremely Large Telescope (ELT), would see the light pollution above it increase by a minimum of 5%. This increase already represents a level of interference incompatible with the conditions required for world-class astronomical observations. The impact on the skies above the CTAO-South, located just 5km from INNA, would be the most significant, with light pollution going up by at least 55%.
“Any loss in the quality of the Chilean night skies over Paranal — no matter how small — should not be tolerated, as any science lost will be gone forever and can never be recovered,” states Roberta Zanin, CTAO Project Scientist.
For its technical analysis, a team of experts led by ESO Director of Operations Andreas Kaufer joined forces with Martin Aubé, a world-leading expert on sky brightness at astronomical sites, to run simulations using the most advanced light-pollution models. As input, the simulations used publicly available information provided by AES Andes when submitting the project for environmental assessment, which states the complex will be illuminated by over 1,000 light sources.
“The light-pollution figures we are reporting assume that the project will install the most modern available luminaries in a way that minimises light pollution. However, we are concerned that the inventory of light sources planned by AES is not complete and fit for purpose. In that case our already alarming results would underestimate the potential impact of the INNA project on the Paranal sky brightness,” explains Kaufer.
In addition to the dark and clear skies, Paranal Observatory is the world’s top site for astronomy thanks to its exceptionally steady and stable atmosphere – it has what astronomers call excellent seeing conditions or very low “twinkling” of astronomical objects caused by turbulence in Earth’s atmosphere. With INNA, the best seeing conditions could deteriorate by up to 40%, in particular due to the air turbulence caused by the project’s wind turbines.
Another worry is the impact of the vibrations caused by INNA on the VLT Interferometer (VLTI) and the ELT, which are both extremely sensitive to micro-seismic noise. The technical analysis reveals that INNA’s wind turbines could produce an increase in these micro-vibrations of the ground that is large enough to impair the operations of these two world-leading astronomical facilities. Dust during construction is also problematic as it settles on the telescope mirrors and obstructs their view.
Furthermore, INNA’s infrastructure is likely to encourage the development of an industrial hub in the area, which could turn Paranal into an unusable site for top-level astronomical observations.
“ESO and its Member States are fully supportive of energy decarbonisation. For us, Chile should not have to make a choice between hosting the most powerful astronomical observatories and developing green-energy projects. Both are declared strategic priorities by the country and are fully compatible — if the different facilities are located at sufficient distances from one another,” says ESO Director General Xavier Barcons.
The full technical report will be submitted to the Chilean authorities later this month as part of the Citizen Participation Process (PAC) in INNA’s environmental impact assessment and made public at that time. In addition to their press release, ESO is making an executive summary of the report public in advance.