A global push has filled the hole in the ozone layer. Satellites could threaten it.

Low Earth orbit, a layer of superhighways that runs around Earth’s thermosphere at an altitude of 200 to 600 miles above our heads, has recently become overloaded.

Still, no one knows how the massive increase in the number of satellites orbiting Earth will affect the atmosphere, and thus life below. With the rush to send more and more satellites into orbit, a new study suggests that the hole in the ozone layer, a problem scientists thought they had solved decades ago, could be making a comeback.

“Until a few years ago, this wasn’t an area of ​​research at all,” Martin Ross, an atmospheric scientist at Aerospace Corporation, said of the study, which looked at how a potential increase in man-made metal particles could damage Earth’s protective layer.

Since Sputnik, the first man-made space satellite, was launched in 1957, scientists have thought that when satellites reenter our atmosphere at the end of their lives, their evaporation has little impact. But new satellites — much more advanced, but also smaller, cheaper and more disposable than earlier satellites — have a turn of events that resemble fast fashion, said the study’s lead author, José Pedro Ferreira, a doctoral student in aerospace engineering at the University of Southern California.

Nearly 20 percent of all satellites ever launched have re-entered Earth’s atmosphere in the past five years, where they burned up in rapid, hot flames.

Mr. Ferreira calculated that upon satellite return, most of a burned satellite could become alumina, a pollutant that could disrupt the chemistry of the stratospheric ozone. Each satellite can generate just under 70 pounds of aluminum oxide nanoparticles.

The study, which was based on laboratory measurements and computer models, suggests that if the number of satellites launched results in mega-constellations of hundreds or thousands, they could create a surplus of aluminum 640 percent above natural levels, potentially leading to significant ozone depletion.

“We are only at the beginning of a large research project, so it is too early to know for sure that there is a negative impact, but we are starting to see clear evidence,” said Mr Ferreira, whose research, published in Geophysical research letterswas funded by NASA and the National Science Foundation.

Mr Ferreira said that such studies were not anti-satellite, but complemented the growing body of research into the sustainable development of space.

Daniel Cziczo, a professor of earth, atmospheric and planetary sciences at Purdue University, flies high-altitude planes to view the particles left in the atmosphere by meteorites. Last year he published one study which showed that these particles coagulated with man-made metals from satellites.

He said Mr Ferreira’s study reached conclusions not supported by his own research, by applying the wrong size, composition and chemistry to the particles found in the atmosphere.

Increasing the number of launches and retiring more satellites that are largely burning out will release more material into the atmosphere, Dr. Cziczo. “It raises the question of what impact that will have, and we don’t know yet.” He said ozone depletion and the climate impacts of satellites needed to be studied, but he felt this article did not address those issues appropriately.

Mr Ferreira said: “Models are only as good as the data you can validate them with, so we have to be careful and diligent about the level of certainty we have about the environmental impact.”

Regulators are slowly beginning to notice the unanswered questions that come with increasing space hardware. In 2019, the United Nations Committee on the Peaceful Uses of Outer Space published long-term sustainability guidelines which recommended regulating the environmental impacts of space activities on the planet. In 2022, the Federal Communications Commission, which licenses most satellites, will approved 7,500 of the batch of nearly 30,000 satellites requested by SpaceX.

The Montreal Protocol, an international agreement that regulated ozone-depleting substances in 1987, was written to cover gases, not particles, said Dr. Ross of Aerospace Corporation. But the regulator could intervene in the coming years.

“This is something that the world really needs to take seriously, and the Montreal Protocol is aware of this and will be studying this,” said David Fahey, co-chair of the Montreal Protocol’s Scientific Assessment Panel and director of the Chemical Sciences Laboratory at the National Oceanic and Atmospheric Administration.

The Protocol, he said, would examine the issue for their next review, due to be completed in 2026.