Concentrations of ozone-damaging aluminum oxides in Earth's atmosphere could increase by 650% in the coming decades due to a rise in the number of defunct satellites burning up during reentry, a first-of-a-kind study has found. And, as satellite megaconstellations continue to pique the interests of private companies, this could be pretty bad news for our planet's protective shield known as the ozone layer.
The authors of the study say rising concentrations of satellite-induced pollutants could cause "potentially significant" ozone depletion and thus thwart the ozone layer's slow and steady recovery.
The ozone layer needs to recover in the first place because, in the 1980s, a hole in this layer opened up above Antarctica due to the use of chlorine- and fluorine-rich gases in refrigerants and aerosol sprays. The hole is on the mend, however, 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 hurdle because of a new human-made threat: the megaconstellations. In short, megaconstellations are conglomerates of hundreds (sometimes thousands) of individual satellites working together.
In recent years, scientists have begun voicing concerns about increasing numbers of satellites burning up in Earth's atmosphere. Spacecraft bodies are made of aluminum, which gives rise to ozone-destroying aluminum oxides when incinerated. 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 estimate the evolution of their concentrations based on the forecasted proliferation of satellites.
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"This study used atomic scale molecular dynamics simulation to quantify the amount of aluminum oxide generated for a model satellite reentry, and then used the number of reentering satellites planned for satellite megaconstellations to predict the amount of aluminum oxide that will be generated in the future," Joseph Wang, a professor of Astronautics and Aerospace and Mechanical Engineering at USC and the 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 rise even higher with the growing number of launched and reentering satellites.
According to the European Space Agency, about 12,540 satellites currently orbit Earth, out of which around 9,800 are operational. By the end of this decade, that number could increase tenfold due to plans of private companies to build mega-constellations of tens of thousands of internet-beaming, low Earth orbit satellites. SpaceX's Starlink megaconstellation, for instance, currently comprises more than 6,000 spacecraft, and the company has plans to deploy up to 40,000 satellites in total for the endeavor. Firms including OneWeb, Amazon and Chinese projects G60 and Guowang are developing their own mega-constellations.
If all those plans come to fruition, up to 3,200 metric tons of satellite bodies could be burning up in the atmosphere every year by the 2030s. As a result, 630 metric tons of aluminum oxides could be released into the upper atmosphere per year, the researchers estimated, leading to an up to 650% increase in the 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 vaporizes, to reach the altitudes where the ozone layer resides. Only then would the oxides begin their devastating work. The researchers did not study the impact on the protective ozone shield in detail. They did, however, emphasize 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). The ozone absorbs harmful ultraviolet (UV) radiation, protecting living organisms on the planet's surface from damage.
Unlike the traditional ozone-depleting substances, aluminum oxide particles trigger ozone destruction processes without getting consumed in the reactions, the researchers said. The concentrations of these substances therefore remain stable, allowing the oxides to continue their harmful work, until they naturally descend to lower altitudes below the ozone layer. That may, however, also take up to 30 years, Wang said.
Although much more meteorite material than artificial satellites enters Earth's atmosphere every year, this natural space rock contains no aluminum and therefore doesn’t pose any risk to the ozone layer. The researchers said that more research is needed to fully understand the risks megaconstellations pose to our planet.
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"The chemistry and physics of these reentry byproducts as they cool down and settle in the atmosphere, including chemical reactions with ozone, are not the subject of this study and are not completely understood by the community," José Pedro Ferreira, a research fellow at USC and lead author of the study told Space.com in an email. "For that reason, any conclusions related to environmental impacts are premature. These known unknowns should work as an incentive to devote more resources to this research line, which is currently being pursued by our group at USC."
The study was published in the journal Geophysical Research Letters on June 12.
