Top line
A new study from the European Southern Observatory warns that plans to launch more than 1.7 million satellites into orbit could have “disastrous consequences for astronomy”, making the night sky brighter and reducing scientists’ ability to observe the galaxy and the universe. SpaceX is set to create a new economy in low Earth orbit by expanding its current Starlink telecommunications constellation and adding orbital AI data centers and even wirelessly transmitted solar power from space. The study – only the latest to warn of the scientific and environmental dangers of crowding Earth’s orbit – concludes that Earth’s orbit should not be limited to more than 100,000 faint satellites, all below naked-eye visibility, to protect modern terrestrial astronomy. According to Orbital Radarthere are currently 17,501 satellites in Earth orbit — 10,000 of them active SpaceX Starlink satellites.
This image shows satellites crossing the night sky over the northern Atacama Desert in Chile over the course of just one hour. This is a stack of a time-lapse video taken on October 15, 2025 about two hours after sunset. Some streaks are caused by airplanes and can be easily identified by their flashing lights, but most streaks are caused by satellites. In the foreground we see the dome of ESO’s Extremely Large Telescope (ELT), the world’s largest optical/infrared telescope, under construction atop Cerro Armazones. Behind it we see the lasers of ESO’s Very Large Telescope (VLT) at the Paranal Observatory, 22 km away from the ELT.
F. Kamphues, ESO/M. Kornmesser
Key Facts
The judges researchled by ESO astronomer Olivier Hainaut and accepted for publication at Astronomy & Astrophysicsis the first to calculate how large and bright satellite constellations could affect astronomical observations by increasing the brightness of the background sky.
As of 2019, the number of active Earth-orbiting satellites has grown rapidly, largely led by SpaceX’s Starlink network. The proposed constellations could push that number much higher.
SpaceX has plans to launch 20,000 Starlink satellites. It currently has 10.3 million subscribers in 164 countries. It has also filed plans to send an additional million satellites into orbit for space-based data centers.
Other projects, such as Reflect Orbital, E-Space’s Cinnamon constellation, and China’s CTC-1 and CTC-2 systems, could add hundreds of thousands more satellites.
The global space economy is projected to grow from about $630 billion in 2023 to $1.8 trillion by 2035, according to World Economic Forum. This is about twice the growth rate of global GDP.
Bright satellites will change the night sky
“So far we’ve made it, but it’s getting worse” he said Hainaut, astronomer at ESO for more than 30 years. Although some companies have taken steps to reduce the brightness of satellites, he warned that current proposals push the limit of what astronomy can handle.
Sunlit satellites can leave bright streaks in telescopic images, blocking out faint galaxies, Earth-like exoplanets and potentially hazardous asteroids. Hainaut discovered that SpaceX’s mega-constellation could produce dozens of satellite trails in images taken by ESO’s Very Large Telescope in Chile two hours after nightfall. This could cause visual field losses of up to 28%. Since they reflect light from the sun when they are just below the horizon, it is always just after sunset and just before sunrise that satellites cause the most problems. Wide-field cameras, like the one at the Vera C. Rubin Observatory, could be even more vulnerable. A bright satellite trail can saturate detectors, create ghost trails, and potentially render images unusable.
This image shows how sunlight scattered by Reflect Orbital’s space mirrors would increase the overall brightness of the sky above ESO’s Very Large Telescope (VLT). The left image was taken with an all-sky camera on a moonless night on May 16, 2026. North is up and west is on the right. The domes housing the VLT’s four 8-meter telescopes can be seen at top right. The image on the right is a simulation showing how much brighter the sky would be with the Reflect Orbital’s full constellation of 50,000 mirrors. Although the mirrors are not pointed directly at the observatory, they still scatter light to the side, which is then further scattered by the atmosphere. As a result, the sky would be up to three to four times brighter.
ESO/O. Hainaut
Mirror Orbital’s ‘Sunlight On Demand’ plans
The study raises particular concern for Reflect Orbital, a US startup that designs large mirror-like satellites designed to provide sunlight at night. The company plans to launch a prototype soon and expand to 50,000 satellites by 2035. Hainaut’s calculations show that these satellites could become the brightest objects ever put into orbit. Through a reflected beam, a satellite could appear four times brighter than the full moon. Even when not aimed directly at an observer, any satellite can appear as bright as Venus. From a city with light pollution, its satellites would be the only “stars” visible in the night sky.
Strict boundaries are required
Hainaut argues that the worst effects can only be avoided by limiting the total number of satellites, existing and future, to about 100,000. He also stresses that the satellites must be fainter than optical magnitude 7 so that they remain invisible to the naked eye even under dark skies. Although they can be this bright immediately after launch, Starlinks typically dim to magnitude 5.5 once they reach their operational orbit, according to Journal of Astronomy.
SpaceX and Reflect Orbital have each filed with the US Federal Communications Commission (FCC) for a launch license. “The FCC received over 1,800 comments on Reflect Orbital and nearly 1,500 comments on the application from SpaceX,” said Betty Kioko in ESO’s Office of Institutional Affairs. “The ball is now in the FCC’s court, and we wait to see what decisions they make on both files. For optical astronomy, this is an existential threat, and we hope that regulators will share that view.”
