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ESO Study Warns Mega‑Constellations Could Make Ground Optical Astronomy Unviable

The study quantifies how vast increases in low‑Earth‑orbit satellites, including proposed reflective 'mirror' craft, would raise night‑sky brightness and trail rates that degrade major telescopes' data.

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Overview

  • The European Southern Observatory published the modelling study on July 1, 2026 showing that large planned fleets of LEO satellites would sharply reduce telescope sensitivity and usable observing time.
  • There are about 14,000 satellites in orbit today and operator plans examined in the study could add as many as 1.7 million more, a scale the authors say would overwhelm dark‑sky conditions.
  • Reflective 'mirror' satellites proposed by companies such as Reflect Orbital would be unusually bright and could appear like thousands of Venus‑like points or moon‑bright streaks, causing disproportionate damage to images.
  • The ESO and professional societies have submitted the findings to the U.S. FCC; companies have offered partial fixes such as darker coatings and exclusion zones but the study concludes those efforts are likely insufficient without strict numerical and brightness caps.
  • Major telescopes such as the VLT and the Vera C. Rubin Observatory could lose large fractions of usable data, and the broader risks include more orbital crowding, debris, and increased launch and reentry pollution that will affect communities and research worldwide.