by The amount of ozone-depleting aluminum oxides in the Earth’s atmosphere could increase by 650% in the coming years due to an increase in the number of non-gaseous satellites burning up during re-entry, a first-of-its-kind study has found . And, as satellite mega-constellations continue to squeeze the interests of private companies, this could be bad news for our planet’s protective shield known as the ozone layer.
The authors of the study say that increased concentrations of satellite-transmitted pollutants could cause “potentially significant” ozone depletion and hinder the slow and steady recovery of the ozone layer.
The ozone layer must be recovered first because, in the 1980s, a hole opened in this layer over Antarctica due to the use of gases rich in chlorine and fluorine in refrigerants and aerosol sprays. The hole is closing, 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 could be a major obstacle to soon because of a new man-made threat: the mega-constellations. In short, mega-constellations are conglomerates of hundreds (sometimes thousands) of individual satellites working together.
For a few years now, scientists have begun to express concern about the increasing number of satellites burning up in the Earth’s atmosphere. Spacecraft bodies are made of aluminum, which causes ozone to destroy aluminum oxides when burned. The new study, carried out 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 to estimate the evolution of their concentration based on the predicted proliferation of satellites.
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“This study used atomic-scale molecular dynamics simulations to quantify the amount of aluminum oxide generated for a model satellite reentry, and then used the number of reentry satellites intended for satellite megasolutions to estimate the amount of aluminum oxide to predict what will be generated in the future,” Joseph Wang, professor of Astronomy and Aerospace and Mechanical Engineering at USC and corresponding author of the study, told Space.com.
The researchers found that about 332 metric tons of old satellites burned up in the atmosphere in 2022, generating 17 metric tons of aluminum oxide particles in the process. Between 2016 and 2022, the concentration of these oxides in the atmosphere increased by eight times and will continue to rise even higher with an increase in the number of launch and re-entry satellites.
According to the European Space Agency, approximately 12,540 satellites currently orbit the Earth, of which approximately 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 thousands of low-orbit Internet-beaming satellites. For example, SpaceX’s mega constellation consists of more than 6,000 spacecraft, and the company 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-stars.
If all those plans are carried out, 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 increase of up to 650% in the concentration of these particles compared to natural levels .
Wang said that it takes up to 30 years for the particles, which first accumulate at an altitude of about 50 miles (85 kilometers) when most of the satellite material vaporizes, to reach the altitude where the ozone layer is . Only then would the oxides begin their destructive work. The researchers did not study the impact on the protective ozone layer in detail. They stressed, however, that the effects could be “significant.”
Most of the ozone protects the planet 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 damage.
Unlike traditional ozone-depleting substances, aluminum oxide particles stimulate ozone-depleting processes without being consumed in the reactions, the researchers said. So the concentration of these substances remains stable, allowing the oxides continue on their harmful work, until they naturally descend to lower altitudes under the ozone layer. That, however, could take up to 30 years, Wang said.
Although much more meteorite material than artificial satellites enters the Earth’s atmosphere each year, this natural space rock contains no aluminum and therefore poses no threat to the ozone layer. The researchers said that more research is needed to fully understand the risks that mega-stars pose to our planet.
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“The chemistry and physics of these reentry by-products 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 public,” José Pedro Ferreira, research member at USC and lead author of the study told Space.com in an email. “For that reason, any conclusions related to environmental consequences are premature. These unknowns should act as an incentive to devote more resources to this line of research, which our group is pursuing at USC right now.”
The study published in the journal Geophysical Research Letters on 12 June.
