ESO warns 1.7M planned satellites would wreck ground-based astronomy

A new peer-reviewed European Southern Observatory study, authored by astronomer Olivier Hainaut, models what would happen if the 1.7 million satellites now proposed for low-Earth orbit actually launched — and concludes the effects on astronomy would be devastating. Roughly 14,000 satellites orbit today, dominated by Starlink, but planned constellations dwarf that: SpaceX alone wants a million more for space-based data centres, while E-Space’s Cinnamon and China’s CTC-1/2 would add hundreds of thousands. Simulating satellite positions, motion, and brightness, Hainaut found dozens of bright trails per exposure on ESO’s Very Large Telescope, costing up to 28% of its field of view; slightly brighter satellites could render most images from the Vera C. Rubin Observatory unusable for hours each night.

The standout threat is Reflect Orbital, a startup planning 50,000 mirror satellites that beam reflected sunlight to Earth. These would be the brightest objects ever put in orbit — appearing four times brighter than the full Moon to anyone inside a beam, and as bright as Venus otherwise — and would raise overall sky brightness three- to fourfold. Crucially, the study is the first to account not just for satellite streaks but for diffuse and scattered light that brightens the entire background sky, the harder-to-escape form of light pollution.

Hainaut argues the total population of existing and future satellites should be capped at 100,000, all fainter than visual magnitude 7 (below naked-eye visibility); any brighter and the ceiling must drop sharply. The stakes are regulatory, not just scientific: SpaceX and Reflect Orbital have both filed with the FCC, drawing roughly 1,500 and 1,800 public comments respectively, and ESO — with the Royal Astronomical Society and IAU — has formally urged the agency to treat unchecked orbital brightening as an existential threat to optical astronomy.