Satellite constellations can have “devastating consequences for astronomy,” study says

The study, carried out by ESO and published on Wednesday in the journal Astronomy & Astrophysics, is the first to assess the extent to which large, very bright satellite constellations – which also raise concerns about their impact on health and the environment – would affect astronomical observations by brightening the night sky.

Since 2019, the number of satellites in orbit around the Earth has increased rapidly to reach 14,000mostly Starlink telecommunications satellites, from SpaceX.

And this is just the beginning. Elon Musk’s company plans to put one million additional satellites into orbit, destined for space data centers.

Other projects, such as “Cinnamon” by the startup E-Space or the Chinese constellations CTC-1 and CTC-2, would add several hundred thousand more satellites to Earth orbit.

Not counting Reflect Orbital, an American startup that intends to launch, by 2035, up to 50,000 large, mirror-like satellites, with the aim of providing sunlight at night using beams of reflected light.

In total, more than 1.7 million satellites could orbit our planet, saturating the night sky that ground-based telescopes try to observe.

“When a satellite passes in front of what we are observing, it leaves a luminous trail in our image, hiding everything behind it,” explains Olivier Hainaut, ESO astronomer and author of the study.

“For some years now this has been happening daily, but it is still bearable. However, If we go from 14,000 to 1.7 million satellites, we are really going to have problems“, declared the researcher to AFP, showing special concern for those designed to be extremely bright.

Even when they do not point their mirrors directly at the observer, the light scattered by the Reflect Orbital satellites would make them appear in the sky like thousands of Venus, the famous highly visible star, known as the “morning star.”

“Whether in Auvergne, in the Sahara or in the Atacama Desert, the sky would cease to be a pure sky and would resemble that observed on the outskirts of a city,” explains the researcher.

To avoid dramatic consequences for terrestrial astronomy, the study argues that the number of satellites in orbit should be limited to 100,000 and that these should be dim enough to not be visible to the naked eye from a dark location.

The study formed the basis for a report presented by ESO, in collaboration with the Royal Astronomical Society of the United Kingdom and the International Astronomical Union, to the Federal Communications Commission (FCC) of the United States, the body in charge of examining the authorization applications submitted by SpaceX and Reflect Orbital.

“The ball is now on the FCC’s side and we look forward to seeing what decisions it will make regarding these two files. For optical astronomy this is an existential threat and we hope that regulators share this point of view,” Betty Kioko, head of institutional affairs at ESO, said in a statement.

“Astronomers have absolutely nothing against the use of satellites. The question is how to coexist,” stresses Hainaut, mentioning a “reasonably good collaboration with satellite manufacturers, in particular with SpaceX,” which “are making a great effort to minimize the impact of their satellites.”

A spokesperson for Reflect Orbital told AFP that the company commissions independent studies from third parties on the impact of its technology and pledged to “continue dialogue with astronomers.”

“By default, our satellites will be ‘off’” and “we will systematically avoid redirecting light near observatories,” he added.

Light pollution generated by satellite constellations is not just a concern for astronomers. It can also have repercussions on health and the environment, by altering the biological clocks of living beings and ecosystems.

Furthermore, large satellite constellations have a direct impact on air quality, both during their launch and upon re-entry into the atmosphere at the end of their useful life.