ESO warns megaconstellations could flood night sky with light

The European Southern Observatory (ESO) has published a study in *Astronomy & Astrophysics* warning that planned megaconstellations of up to 1.7 million satellites could dramatically brighten the night sky and impair ground‑based astronomy. Current low‑Earth‑orbit traffic already exceeds 14 000 objects, dominated by SpaceX’s Starlink, and several companies have filed applications for additional launches: SpaceX aims for an extra million satellites for space‑based data centres, Reflect Orbital proposes up to 50 000 large, mirror‑like satellites, while Chinese projects CTC‑1 and CTC‑2 and the European startup E‑Space’s “Cinnamon” could add hundreds of thousands more.

ESO astronomer Olivier Hainaut explained that a passing satellite “leaves a bright trail on the image, obscuring everything behind it,” and that diffuse reflections could raise background brightness, potentially causing up to a 28 % loss of usable field for instruments such as the Very Large Telescope and seriously compromising the upcoming Vera Rubin Observatory. The study recommends limiting the total number of satellites to about 100 000 and ensuring they are faint enough to remain invisible to the naked eye from dark sites.

The findings have been forwarded to the U.S. Federal Communications Commission, which now faces pressure to weigh scientific concerns against commercial launch plans. ESO officials emphasized that the issue also touches on broader health and environmental impacts, citing potential disruption of biological clocks and air‑quality effects from launches and re‑entries.