Proposals to install reflective mirrors and satellites up to 1m into low Earth orbit could have major implications for human health and the environment, leading sleep and circadian rhythm researchers have said.
The presidents of four international scientific societies representing about 2,500 researchers from more than 30 countries are among those who expressed their concern in letters to the US Federal Communications Commission (FCC).
The commander is considering plans to start Reflect Orbital to illuminate parts of the Earth at night using reflective satellites, as well as equipment from SpaceX that can expand the number of satellites in the lower part of the Earth.
“The proposed scale of the circulation will represent a major change in the night light environment at the level of the planet,” said 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.
They said that changing the light-dark cycle can disrupt the biological clocks that control sleep and hormone production in humans and animals, the migration of nocturnal species, the seasonal cycle of plants and the rhythms of marine phytoplankton that support marine food webs.
They urged authorities to conduct a comprehensive environmental assessment and set limits on satellite reflectivity and night sky light. Professor Charalambos Kyriacou, a geneticist at the University of Leicester and president of EBRS, said: “We say, please think before you go ahead with this, because this could have global consequences for things like food security. Plants need night, you can’t just get rid of them.”
Reflect Orbital hopes to use satellites equipped with large reflective mirrors to direct sunlight into areas about 5km to 6km wide “on demand”, with the light changing “from full moon to high noon”. The company says the system can extend solar energy production until evening and provides lighting for construction projects, disaster response and agriculture, with light provided only in areas approved by local authorities.
Meanwhile, SpaceX has proposed launching up to 1m satellites to create a massive solar-powered computer network in orbit designed to run a range of artificial intelligence tasks. The company says the system can reduce the power and cooling needs of the world’s facilities.
Ruskin Hartley, executive director and chief executive of DarkSky International, a non-profit organization focused on protecting the natural night sky, who also wrote to the FCC, said: “Although ideas such as satellite mirrors that shine ‘sunlight on demand’ on Earth or constellations up to 1m for AI datacentres may sound like science fiction.”
He added: “Scientific studies have shown that the number of satellites orbiting the earth has increased the total night sky brightness, or sky brightness, by about 10%.”
The satellites affected the night sky in two main ways, Dr Miroslav Kocifaj, of the Slovak Academy of Sciences, Bratislava, said. Individual satellites would leave streaks in telescope images, while sunlight reflected by satellites and debris lit up the sky.
His model suggests that these things already add between 3 and 8 microcandela per square meter to the brightness of the night sky. By 2035, he predicts that this could rise to between 5 and 19 microcandela, approaching the threshold that astronomers have set for maintaining a naturally dark sky.
Although this additional light is still much lower than that of the moon, “what I can say with confidence is that this phenomenon is real, that it is global and will not escape by moving to a distant place, and that it will increase significantly in the next ten years if the current methods of satellite production and waste production continue”, Kocifaj said.
Professor Tami Martino, of the University of Guelph, who is the president of the Canadian Society of Chronobiology, said that when it comes to the effects of life on Earth, “the real question is not the brightness compared to the brightness of the moon, but whether biological systems can detect the change”.
“Circadian systems are sensitive to light levels well below what humans perceive as bright,” Martino said. If the sky is permanently bright, the effects may affect the environment in ways we do not yet fully understand.
A separate letter from the presidents of the World Sleep Association, the European Sleep Research Association, the Sleep Foundation, the Australian Sleep Association and the Australasian Chronobiology Society said “circulatory disruption is not just a disturbance; it is a physiological process that causes negative health effects”.
The letter added: “We are not arguing against the creation of space,” saying that changing the night sky should be taken with the same seriousness as other changes in the state of the planet’s environment, such as climate change and ocean acidification. “The alternation of light and dark is not a trivial situation. It is one of the oldest organizing principles of life on Earth.”
Hartley said that as the number of satellites increases, fast-moving artifacts may become a prominent feature of the night sky. He said: “There can be times and places where satellites pass the visible stars in abundance. Many birds and other insects used the stars to travel, and the human experience of the night sky can also change dramatically.
Reflect Orbital projects will also introduce a new type of light pollution with many unstudied effects, including potential public safety risks, Hartley said. “As these rays travel across the country, there is the possibility of strong or blinding rays, especially if the systems are not working properly or they are moving far from the target”.
Reflect Orbital declined to comment, while SpaceX did not respond to a request for comment.
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