The rapid expansion of low Earth orbit satellites is fueling concerns about ozone layer depletion. In January, around 120 SpaceX Starlink satellites burned up in Earth’s atmosphere, creating artificial meteor showers. While these displays may look stunning, scientists warn that the re-entry of satellites releases aluminum oxide particles, which could pose a long-term risk to the ozone layer.
The Growing Satellite Problem
Satellites in low Earth orbit (LEO) have an operational lifespan of about five years. After that, they are decommissioned and left to re-enter Earth’s atmosphere, where they burn up due to friction. Starlink alone has launched nearly 8,000 satellites since 2019, with approval for 12,000 more and plans for up to 42,000 in the future. Other companies, including Amazon, are also launching thousands of satellites.
As more satellites fall back to Earth, scientists worry about the increasing presence of metals in the atmosphere. The European Space Agency (ESA) estimates that more than 28,000 objects are currently in orbit, with most in LEO.
What Happens During Re-Entry?
When a satellite re-enters, it travels at around 27,000 km per hour, colliding with the dense atmosphere. The extreme heat generated by aerodynamic friction causes the satellite to disintegrate, with most components vaporizing. While this process prevents debris from reaching Earth’s surface, it is not environmentally neutral.
Satellites contain large amounts of aluminum, which oxidizes during re-entry, forming aluminum oxide nanoparticles. A typical Starlink satellite, weighing around 250 kg, produces approximately 30 kg of aluminum oxide. These microscopic particles remain suspended in the upper atmosphere for long periods.
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How Aluminum Oxide Affects the Ozone Layer
Re-entry typically occurs in the mesosphere, 50 to 80 km above Earth. The concern is that aluminum oxide particles eventually descend into the stratosphere, home to the ozone layer. The ozone layer protects life on Earth by absorbing harmful ultraviolet radiation.
Studies suggest aluminum oxide can act as a catalyst for ozone-destroying reactions, similar to how chlorofluorocarbons (CFCs) caused ozone depletion in the past. Unlike CFCs, aluminum oxide does not directly destroy ozone, but it accelerates chemical reactions that break down ozone molecules. One particle of aluminum oxide could potentially contribute to the destruction of thousands of ozone molecules over decades.
Evidence of Atmospheric Pollution
NASA’s 2023 high-altitude tests over Alaska confirmed that satellite re-entries release metals, including aluminum, into the atmosphere. Researchers found that aluminum oxides in the stratosphere increased eightfold between 2016 and 2022, aligning with the rise in satellite launches.
In 2022 alone, re-entries released 41.7 metric tonnes of aluminum, far exceeding natural sources like micrometeoroids, which contribute only 16.6 metric tonnes annually. If satellite launches continue at this pace, aluminum oxide emissions could reach 360 metric tonnes per year, a 646% increase over natural levels.
Future Risks and Possible Solutions
The long-term impact of satellite re-entries is concerning. Scientists estimate that aluminum oxide particles may take 20 to 30 years to reach the ozone layer. By the time measurable ozone depletion is detected, the atmosphere could already be oversaturated with these particles, leading to delayed or even reversed ozone recovery.
Despite the risks, current regulations do not address ozone depletion from satellite re-entries. The U.S. Federal Communications Commission (FCC) grants licenses for satellite mega-constellations without considering their atmospheric impact. Similarly, commercial satellites are excluded from environmental reviews under the National Environmental Policy Act (NEPA).
Global efforts for space sustainability remain slow. The United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) has begun discussions, but no binding international agreement exists on pollution from re-entering satellites.
A Call for Action
Experts suggest several solutions. Satellite manufacturers could develop alternative materials that do not release aluminum oxide upon re-entry. Another approach is boosting satellites into graveyard orbits, where decommissioned satellites remain in space instead of burning up in the atmosphere. However, this method requires more fuel and may only delay the problem.
With thousands of satellites set to launch in the coming years, urgent action is needed to address this growing environmental challenge. The long-term health of the ozone layer may depend on how the space industry manages its impact on Earth’s atmosphere.
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