A new study by the European Southern Observatory (ESO) warns that current plans to deploy more than 1.7 million satellites in Earth's orbit could cause serious damage to ground-based astronomy. To preserve the capabilities of modern telescopes, the total number of spacecraft in low Earth orbit should remain below 100,000, provided the satellites maintain low visibility.
Since 2019, the number of satellites in orbit has grown rapidly and now exceeds 14,000, largely because of Starlink, developed by SpaceX. The situation could change dramatically in the coming years as additional large-scale projects move forward.
Satellite Expansion Could Reshape the Night Sky
Beyond SpaceX's plans for orbital data centers, several other initiatives are under development, including E-Space with its Cinnamon constellation, as well as China's CTC-1 and CTC-2 systems. Together, these projects involve the launch of hundreds of thousands of additional satellites.
Researchers expressed particular concern over the startup Reflect Orbital, which intends to deploy up to 50,000 large mirror-equipped satellites by 2035. The company aims to illuminate the night sky with reflected sunlight.
Calculations indicate that even when the reflected beams do not point directly toward observers, each satellite could appear as bright as Venus. At the center of the beam, brightness could exceed the full Moon by a factor of four. In heavily light-polluted cities, these objects could become the only clearly visible "stars" in the sky.
Modern Telescopes Could Lose Large Amounts of Data
The study modeled the trajectories and brightness of both existing and planned satellite systems.
Results show that at the Paranal Observatory in Chile, observations using the Very Large Telescope (VLT) would record dozens of bright streaks in every image captured two hours after sunset. Such interference could reduce usable viewing areas by as much as 28 percent.
Wide-field survey telescopes may experience even greater disruptions.
Even satellites invisible to the naked eye create diffuse light effects that increase the overall brightness of the night sky. Estimates suggest that a complete Reflect Orbital constellation could make the sky three to four times brighter.
Such changes would complicate observations of distant galaxies, Earth-like exoplanets, and potentially hazardous asteroids.
Scientists Call for Limits on Satellite Numbers
The study recommends limiting the total number of satellites in orbit to approximately 100,000 in order to preserve astronomical research capabilities.
Researchers also propose that satellites remain dimmer than seventh-magnitude stars so they cannot be seen with the naked eye. The study notes that this figure serves as a guideline rather than a strict limit, but exceeding these levels could produce data losses comparable to major technical failures.
Researchers also highlighted additional risks linked to large-scale satellite deployment, including potential effects on human biological rhythms, atmospheric pollution caused by satellite re-entry, and reduced air quality.
The authors emphasized that low Earth orbit should be treated as a limited resource requiring responsible management, allowing future generations to benefit from both global connectivity and scientific discovery.
