ESO warns planned 1.7 million satellites pose existential threat to astronomy

Plans to deploy a collective total of 1.7 million satellites into Earth’s orbit represent an existential threat to astronomy and the integrity of the night sky, according to new research published in the journal Astronomy & Astrophysics. The study, led by European Southern Observatory (ESO) astronomer Olivier Hainaut, warns that such an unprecedented swarm of hardware would render significant portions of the heavens inaccessible to modern telescopes.

Proposed constellations, spearheaded by SpaceX’s plan to launch one million satellites to power space-based data centers, along with projects like the “Cinnamon” plans from E-Space, China’s CTC-1 and CTC-2, and a 50,000-satellite constellation from U.S. Startup Reflect Orbital, would push the total toward 1.7 million.

The study marks the first time researchers have computed the specific impact of these constellations on background sky brightness. Hainaut’s simulations indicate that for the largest camera ever built—housed at the Vera C. Rubin Observatory in Chile—most images would become unusable for several hours each night. Reflect Orbital’s proposed fleet, which utilizes massive mirrors to reflect sunlight back to Earth at night, poses a particularly acute risk. Even without their beams pointed directly at an observatory, the scatter from these satellites would render them as bright as the planet Venus, and in cities, they would appear as the only visible "stars" in the sky.

"When a satellite crosses what we observe, it makes a bright streak on our image, zapping whatever is behind it,"

Olivier Hainaut, ESO astronomer, via AFP

To preserve the ability to conduct astronomical research, the ESO team calls for a strict limit of 100,000 total satellites, provided they remain faint enough to be invisible to the naked eye.

The U.S. Federal Communications Commission (FCC) is currently reviewing applications from major operators. The FCC has received more than 1,800 comments regarding Reflect Orbital and nearly 1,500 comments on the SpaceX proposal. Betty Kioko, ESO’s institutional affairs officer, stated that the organization’s research was submitted as part of the formal consultation process.

"The ball is now in the FCC's court, and we wait to see the determinations they make on both filings. For optical astronomy, this is an existential threat, and we hope that the regulators will share that view."

Betty Kioko, ESO Institutional Affairs Officer, via ESO

Reflect Orbital intends to launch a prototype this year, with plans to scale to 50,000 satellites by 2035.