Scientists Warn Reflective Satellites Could Disrupt Global Sleep and Ecosystems
Proposals to deploy reflective mirrors and up to one million additional satellites in low Earth orbit could have profound consequences for human health and ecosystems worldwide, according to leading sleep and circadian rhythm researchers. Presidents of four international scientific societies, representing approximately 2,500 researchers from over 30 countries, have raised concerns in letters to the US Federal Communications Commission (FCC).
Regulatory Considerations and Corporate Plans
The FCC is currently evaluating plans by the start-up Reflect Orbital to illuminate parts of the Earth at night using reflective satellites, as well as applications from SpaceX that could dramatically expand satellite numbers in low Earth orbit. Reflect Orbital aims to use satellites equipped with large reflective mirrors to redirect sunlight onto areas roughly 5 to 6 kilometres wide "on demand," with brightness adjustable from full moon to full noon. The company claims this system could extend solar energy production into the evening and provide lighting for construction projects, disaster response, and agriculture, with illumination delivered only to locations approved by local authorities.
Meanwhile, SpaceX has proposed launching up to one million satellites to create a giant solar-powered computing network in orbit designed to run artificial-intelligence workloads. The company argues this system could reduce the energy and cooling demands of terrestrial datacentres.
Biological and Environmental Impacts
In their letters, the presidents of the European Biological Rhythms Society (EBRS), the Society for Research on Biological Rhythms, the Japanese Society for Chronobiology, and the Canadian Society for Chronobiology stated, "The proposed scale of orbital deployment would represent a significant alteration of the natural night-time light environment at a planetary scale." They warned that altering the light-dark cycle could disrupt biological clocks regulating sleep and hormone secretion in humans and animals, migration in nocturnal species, seasonal cycles in plants, and the rhythms of marine phytoplankton that underpin ocean food webs.
Professor Charalambos Kyriacou, a geneticist at the University of Leicester and president of the EBRS, emphasised, "We're saying, please think before you go through with this, because this could have global implications for things like food security. Plants need the night. You can't just get rid of it."
Sky Brightness and Scientific Evidence
Ruskin Hartley, chief executive and executive director of DarkSky International, a non-profit focused on protecting natural night skies, noted, "While ideas like mirrors on satellites beaming 'sunlight on demand' to Earth or mega-constellations of up to 1 million satellites for AI datacentres may sound like science fiction, these proposals are very real." He added that scientific studies have already shown existing satellites have increased diffuse night sky brightness, or sky glow, by roughly 10%.
Dr Miroslav Kocifaj of the Slovak Academy of Sciences explained that satellites affect the night sky in two main ways: individual satellites can leave streaks in telescope images, while sunlight reflected by satellites and debris brightens the sky. His modelling suggests these objects currently add between 3 and 8 microcandela per square metre to night sky brightness, with predictions of this rising to between 5 and 19 microcandela by 2035, approaching thresholds set by astronomers for preserving naturally dark skies.
Circadian Sensitivity and Health Risks
Professor Tami Martino of the University of Guelph, president of the Canadian Society for Chronobiology, highlighted, "Circadian systems are sensitive to light levels far below what humans typically perceive as bright. If the night sky becomes permanently brighter, the consequences could ripple through ecosystems in ways we do not yet fully understand." A separate letter from the presidents of the World Sleep Society, European Sleep Research Society, Sleep Health Foundation, Australian Sleep Association, and Australasian Chronobiology Society stated, "Circadian disruption is not mere inconvenience; it is a physiological mechanism driving major adverse health consequences."
They emphasised that altering the night sky should be treated with the same seriousness as other planetary-scale environmental changes, such as climate change and ocean acidification, noting, "The alternation of light and dark is not a trivial background condition. It is one of the oldest organising principles of life on Earth."
Public Safety and Future Concerns
Hartley warned that as satellite numbers grow, fast-moving artificial objects could become a dominant feature of the night sky, potentially outnumbering visible stars in some times and places. This could affect many birds and some insects that navigate using the stars, and profoundly alter the human experience of the night sky. Reflect Orbital's plans also introduce a new form of light pollution with largely unstudied consequences, including potential public-safety risks from intense glare or blinding flashes if systems malfunction or drift off target.
DarkSky International is calling for a full environmental review before such proposals move forward. Reflect Orbital declined to comment, while SpaceX did not respond to requests for comment.
