Low Earth orbit, a layer of the information highway that envelops Earth’s thermosphere at an altitude of about 320 to 960 kilometers above our heads, has recently become overloaded.
But no one knows how the huge increase in satellites in orbit around the Earth will affect the atmosphere and, consequently, the life below it. A new study suggests that the hole in the ozone layer, a problem that scientists thought they had solved decades ago, could flare up again in the rush to send more and more satellites into space.
“Until a few years ago, this was not an area of research at all,” said Martin Ross, an atmospheric scientist at the Aerospace Corporation, of the study, which examined how a possible increase in man-made metal particles could destroy the Earth’s protective layer.
Since Sputnik, the first man-made space satellite, was launched in 1957, scientists assumed that the vaporization from satellites re-entering our atmosphere at the end of their life would have little impact. But new satellites – much more advanced, but also smaller, cheaper and easier to dispose of than previous satellites – have sales reminiscent of fast fashion, says the study’s lead author, José Pedro Ferreira, a doctoral student in aerospace engineering at the University of Southern California.
Almost 20 percent of all satellites ever launched have re-entered the Earth’s atmosphere in the last half decade and burned up in super-fast, super-hot flames.
Mr Ferreira calculated that when the satellite re-enters the Earth’s atmosphere, most of the burned satellite could become alumina, a pollutant that could affect the chemistry of stratospheric ozone. Each satellite can generate nearly 30 kilograms of alumina nanoparticles.
The study, based on laboratory measurements and computer models, estimates that mega-constellations of hundreds or thousands of launched satellites could create an aluminum surplus of 640 percent above natural levels, potentially leading to significant destruction of the ozone layer.
“We are at the very beginning of a major research project, so we cannot expect any negative impacts with any certainty. But the first evidence is already there,” said Ferreira, whose research, published in Geophysical Research Letters, was funded by NASA and the National Science Foundation.
Mr Ferreira said studies like his were not anti-satellite in nature but were a contribution to the growing body of research on the sustainable development of space.
Daniel Cziczo, a professor of earth, atmospheric and planetary sciences at Purdue University, flies high-altitude aircraft to study the particles that meteoroids leave in the atmosphere. Last year, he published a study showing that these particles coagulated with man-made metals from satellites.
He said that in his study, Mr Ferreira had drawn hasty conclusions that were not supported by his own research by attributing incorrect sizes, compositions and chemical properties to the particles present in the atmosphere.
The increasing number of launches and the retirement of more satellites, most of which burn up, means more material is entering the atmosphere, Dr. Cziczo said. “That raises the question of what impact that will have, and we don’t know that yet.” He said ozone depletion and the impact of satellites on climate need to be studied, but he doesn’t think this work properly addresses those issues.
Mr Ferreira said: “Models are only as good as the data used to validate them, so we should be cautious and prudent about the level of certainty we have about environmental impacts.”
Regulators are slowly taking note of the unanswered questions that come with increasing space hardware. In 2019, the United Nations Committee on the Peaceful Uses of Outer Space released long-term sustainability guidelines that recommended regulating the environmental impact of space activities on the planet. In 2022, the Federal Communications Commission, which licenses most satellites, approved 7,500 of the nearly 30,000 satellites requested by SpaceX.
The Montreal Protocol, an international agreement that regulated ozone-depleting substances in 1987, was aimed at gases, not particles, according to Dr. Ross of the Aerospace Corporation, but the regulator could step in in the coming years.
“This is something the world should really take seriously, and the Montreal Protocol is aware of it and will be looking into it,” said David Fahey, co-chair of the Montreal Protocol’s Scientific Assessment Panel and director of the National Oceanic and Atmospheric Administration’s Chemical Sciences Laboratory.
The protocol will address the issue, he said, at the next assessment, which is due to be completed in 2026.