Concentrations of ozone-depleting aluminum oxides in Earth’s atmosphere could increase by 650% in the coming decades due to an increase in the number of defunct satellites burning up during re-entry, a first-of-its-kind study has found. And as megasatellite constellations continue to pique the interest of private companies, that could be pretty bad news for our planet’s protective shield known as the ozone layer.
The study’s authors say satellite-induced increases in pollutant concentrations could cause “potentially significant” ozone depletion and thus impede the slow and steady recovery of the ozone layer.
The ozone layer must be recovered in the first place because, in the 1980s, a hole in this layer was opened over Antarctica due to the use of chlorine- and fluorine-rich gases in refrigerants and aerosol sprays. However, the hole is being patched, thanks to the Montreal Protocol that banned those offending substances in 1987. But if the team’s new study is correct, this healing process may soon hit a major roadblock due to a threat new man-made: the megaconstellations. In short, megaconstellations are conglomerations of hundreds (sometimes thousands) of individual satellites working together.
In the last years, scientists are beginning to express concerns about the increase in the number of burning satellites in the Earth’s atmosphere. Spacecraft hulls are made of aluminum, which creates ozone-depleting aluminum oxides when burned. The new study, conducted by researchers from the University of Southern California (USC), Los Angeles, is the first to model the generation of these pollutants in the atmosphere and assess the evolution of their concentrations based on predicted satellite propagation.
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“This study used atomic-scale molecular dynamics simulation to determine the amount of alumina generated for a model satellite reentry, and then used the number of reentry satellites planned for satellite megaconstellations to predict the amount of alumina that will be generated in the future, Joseph Wang, a professor of Astronautics and Aerospace and Mechanical Engineering at USC and corresponding author of the study, told Space.com.
The researchers found that in 2022, about 332 metric tons of old satellites burned up in the atmosphere, generating 17 metric tons of aluminum oxide particles in the process. Between 2016 and 2022, concentrations of these oxides in the atmosphere increased eightfold and will continue to increase even more with the increasing number of launched and re-entered satellites.
According to the European Space Agency, about 12,540 satellites currently orbit the Earth, of which about 9,800 are operational. By the end of this decade, that number could increase tenfold because of plans by private companies to build mega-constellations of tens of thousands of Internet-beaming satellites in low Earth orbit. SpaceX’s Starlink megaconstellation, for example, currently includes more than 6,000 spacecraft, and the company has plans to deploy up to 40,000 satellites in total for the effort. Firms including OneWeb, Amazon and Chinese projects G60 and Guowang are developing their own mega-constellations.
If all these plans come to fruition, up to 3,200 metric tons of satellite bodies could burn up in the atmosphere each year by the 2030s. As a result, 630 metric tons of aluminum oxide could be released into the upper atmosphere annually, the researchers estimated, leading to an increase of up to 650% in concentrations of those particles compared to natural levels.
Wang said it takes up to 30 years for the particles, which first accumulate at an altitude of about 50 miles (85 kilometers) where most of the satellite material evaporates, to reach the heights where the ozone layer resides. Only then would the oxides begin their destructive work. The researchers did not study in detail the impact on the protective ozone shield. However, they noted that the effects could be “significant”.
Most of the planet’s protective ozone is concentrated in the stratosphere at altitudes between nine and 28 miles (15 and 30 km). Ozone absorbs harmful ultraviolet (UV) radiation, protecting living organisms on the planet’s surface from harm.
Unlike traditional ozone-depleting substances, the aluminum oxide particles trigger ozone-depleting processes without being consumed in the reactions, the researchers said. Therefore, the concentrations of these substances remain stable, allowing the oxides to they continue their harmful work, until they naturally descend to lower altitudes below the ozone layer. However, this could take up to 30 years, Wang said.
Although far more meteorite material than artificial satellites enter Earth’s atmosphere each year, this natural space rock does not contain aluminum and therefore poses no threat to the ozone layer. The researchers said more research is needed to fully understand the dangers megaconstellations pose to our planet.
“The chemistry and physics of these reentry byproducts as they cool and settle in the atmosphere, including chemical reactions with ozone, are not the subject of this study and are not fully understood by the community,” José Pedro Ferreira, a researcher at USC and lead author of the study told Space.com in an email. “Therefore, any conclusions about environmental impacts are premature. These known unknowns should act as an incentive to devote more resources to this line of research, which is currently being pursued by our group at USC.” “
STUDIES was published in the journal Geophysical Research Letters on June 12.