Megasatellite constellations could jeopardize the recovery of ozone holes
Pollution from the rising number of satellites burning up in Earth’s atmosphere could threaten our planet’s protective ozone layer
Light trails from low-Earth orbit satellites fill the sky in this long-exposure composite image captured over a period of 30 minutes.
Alan Dyer/VWPics/Alamy Stock Photo
From the ground, Earth’s sky seems boundless and eternal, but the view from above reveals something else: a dangerously thin blue line against the black void, all that stands between our living world and the deadly conditions of space. It is in this vulnerable expanse that scientists now recognize a long-standing danger: pollution from re-entering satellites and other orbital debris. According to a new study, this emerging threat could threaten the delicate balance of our planet’s protective ozone layer.
Without costly, regular reboosting, all satellites in low Earth orbit are destined for a fiery fate – gradually losing altitude until they burn up and disintegrate against the thin outer layers of the atmosphere. Since the beginning of the Space Age, this process has been taken for granted as an easy and consequence-free way to remove Earth’s orbital debris. Now a new study, inspired by the skyrocketing number of new satellites, estimates that alumina pollution from satellites in the sky increased eightfold between 2016 and 2022. More alarmingly, the research suggests that this accumulating debris could damage our protective ozone layer in the atmosphere. “We shouldn’t jump to conclusions,” said José Ferreira, lead author of the study and a researcher at the University of Southern California, “but the numbers are very worrying.” The study appears in a June edition of Geophysical research letters.
The broken shield of the earth
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Ozone, a highly reactive compound made up of three oxygen atoms, is one of the most critical components of Earth’s atmosphere. Tight bonds hold the molecule’s oxygen atoms together, allowing an ozone layer in the stratosphere to absorb most of the harmful ultraviolet (UV) radiation streaming in from space, preventing it from reaching the Earth’s surface. However, ozone is also sensitive to degradation due to human activities. In the 1970s, scientists discovered that chlorofluorocarbons (CFCs) from household products were eating away at a ‘hole’ in the ozone layer, severely weakening its protective effects.
While ongoing efforts to repair the ozone hole have seen remarkable success, a new set of pollutants could reverse that recovery. In a study published last October, scientists discovered unusually large amounts of vaporized metals such as aluminum, copper and lithium accumulating in the stratosphere — an anomaly attributed to rocket launches and satellite reentry. ‘We know that satellites re-enter the atmosphere, heat up, evaporate…[and] somehow these metals end up in the stratosphere,” said Martin Ross, author of that study and an atmospheric scientist and senior project engineer for the Aerospace Corporation. He adds that there is a need for a more comprehensive understanding of the potential scale of pollution – from evaporation to sedimentation in the stratosphere.
A time-lapse view of a bulky satellite component melting and disintegrating during a test in a plasma wind tunnel.
The increasing number of satellites only appears to be exacerbating the peak levels of stratospheric metals. More than 8,000 are already in low Earth orbit, and tens of thousands more are planned, mostly in the form of so-called mega-constellations, such as SpaceX’s Starlink, a system of satellites that provides global broadband internet access. Starlink and other mega-constellations rely on economies of scale; their vast fleet is constantly being renewed with new satellites to replace the old ones burning up in the Earth’s atmosphere. The result is a dramatic increase in the number of rocket launches and spacecraft returns. “There is a widespread assumption that something that burns up in the atmosphere disappears, but of course mass never disappears,” says Michael Byers, Canada research chair in global politics and international law and co-director of the Outer Space Institute.
Inspired by the striking detection of metals in the stratosphere last year, Ferreira and his colleagues examined the extent to which each satellite could contribute metal pollutants. Their research simulated interactions between an incoming satellite and oxygen atoms in the mesosphere, or the middle layer of the atmosphere, which lies above the stratosphere. The work showed that the aluminum from the plunging satellite, heated by the flash, quickly eroded and would react with oxygen to form aluminum oxide. It turns out that this could be very bad news for the ozone in the stratosphere.
In sufficient concentrations, aluminum oxide readily catalyzes the destructive reaction of ozone with chlorine gas, splitting the ozone molecule and reducing the Earth’s UV protection. In addition, because aluminum oxide remains intact in this process, it can continue to react with ozone. The compound’s persistence means that even small amounts have the potential to cause significant long-term effects on the ozone layer. Scaling up their results to current mega-constellations and publicly known plans for future expansions, Ferreira and his co-authors estimate that satellites will have pumped 17 tons of alumina into Earth’s mesosphere in 2022 alone. Chillingly, that influx would increase to around 360 tons of alumina per year if the rapid planned proliferation of mega-constellations continues. The study also modeled the atmospheric dynamics of alumina, showing that it could take up to 30 years for the particles to drift into the stratosphere and wreak havoc on the ozone layer. “While [the pollutant] is accumulating in the atmosphere, it’s time for us to lose. By the time we see the results, it may be too late,” says Ferreira.
Defensive measures
Understanding how infalling space debris depletes the ozone layer is only part of the battle. Should independent studies validate these findings, the next critical challenge will be developing tactics to counter these effects.
The discovery of the ozone hole in the 1970s led to the Montreal Protocol of the following decade, an international treaty that pushed world leaders to successfully combat the CFC problem in the 1980s. But when applied to pollution from satellite re-entry rather than from refrigerators and cans of hairspray, this kind of international treaty seems less a model for solutions and more a damning indictment of gaps in our current regulatory frameworks. The Montreal Protocol has shown that complex environmental problems can be managed with global coordination. However, the existing rules and restrictions on orbital activity appear to offer poor, contradictory prospects for an easy solution. For example, the Federal Communications Commission requires U.S. satellites in low Earth orbit to be removed within five years of mission completion. These regulations are primarily intended to prevent overcrowding in space, but do not take into account possible atmospheric consequences. “It’s an interesting paradox,” says Ferreira. “We need to clean up the orbital environment, but we don’t know what the cost to the atmosphere is.”
Brian Weeden, systems director at the Center for Space Policy and Strategy at the Aerospace Corporation, added: “The current regulatory framework is not built for this kind of thing. There’s no checkbox that says, ‘Also check if this has an impact on the upper atmosphere,’ because this wasn’t an issue that was on anyone’s mind.” Still, satellite launches continue, and as we slowly learn more about the process, “it’s becoming more and more of a problem,” says Ross. “We are blind, but we keep driving on the road.”
Ferreira and his colleagues’ work exposes the increasing invisible pollutants in space that threaten our protective atmosphere. But predicting atmospheric dynamics is one problem, and predicting the global response is potentially an even bigger problem. “I am hopeful that this time we can be faster and smarter than when you look at climate change, for example,” says Leonard Schulz, a researcher at the Institute for Geophysics and Extraterrestrial Physics at the Technical University of Braunschweig in Germany. “We can act quickly [this issue]and we must work together.”