In January more than 100 communications satellites burned up in Earth’s atmosphere, vaporising as they crashed towards the planet at about eight kilometres a second. These spectacular exits are intentional, meant to prevent satellites from clogging up orbital real estate or plummeting to the surface in an out-of-control manner. Three years ago the Federal Communications Commission (FCC), an American agency that approves communications-satellite applications, ordered that all such satellites had to fall out of orbit after five years to reduce space debris. Similar regulations apply elsewhere.
Such “designed demise”, though well-intentioned, has unintended consequences. When satellites vaporise, they seed the stratosphere (the region of the atmosphere between 10km and 50km above Earth’s surface) with particles of constituent metals, including aluminium, copper, lithium and niobium. The quantities were once negligible, but with 11,000 satellites now in orbit—and requests for another 1m launches lodged with the International Telecommunication Union, an agency at the United Nations—the chemistry of the atmosphere could be about to change on a larger scale. “There’s a lot of concern,” said Daniel Murphy, an atmospheric chemist at America’s National Oceanic and Atmospheric Administration, in November. “We’re putting these materials in, we don’t know what they will do, and they’re going to be going in in ever increasing amounts.”
Earth’s atmosphere has been bombarded by foreign bodies, namely meteoroids and cosmic dust, for billions of years. But this is different. According to a white paper released last year by the European Space Agency, the natural influx of matter into the atmosphere is about 12,400 tonnes a year. In 2019, the most recent year for which data are available, humanity added around 890 tonnes, and that mass is rising.
Moreover, “It’s not just total tonnage; it’s a different set of metals,” says John Plane at the University of Leeds. Space debris injects ten times more lithium into the atmosphere than natural cosmic dust, as well as larger quantities of new exotic metals, he says. In a paper published in 2023, Dr Murphy and his colleagues estimated that one in ten aerosol particles in the stratosphere now contains metals from spacecraft ablation.
How long will these particles linger and what will they do? There are reasons to worry. Particles of aluminium, for example, could combine with oxygen to form molecules of alumina, creating a surface on which other larger chemical reactions can take place. One might liberate chlorine—a known destroyer of the ozone, which keeps Earth safe from ultraviolet radiation—from molecules of hydrogen chloride. Other elements, such as copper, are catalysts, capable of speeding up chemical reactions without being consumed themselves. As the concentration of such catalysts continues to grow, they could carry on accelerating reactions indefinitely.
For now, though, there remain more questions than answers. Researchers around the world are trying to fill the gaps in their knowledge. A lack of monitoring equipment is one challenge. Another is a lack of oversight. Most telecommunications satellites, the most common type of spacecraft, are currently launched by SpaceX in America. The company’s Starlink constellation, which includes almost 7,000 machines, accounts for most of the satellites being sent into space. Although the FCC requires all satellites to undergo an environmental review, those that will be part of mega-constellations, consisting of more than 100 satellites, are exempt. In 2022 the Government Accountability Office, a congressional auditor, recommended that the FCC investigate the environmental impact of larger constellations, but the agency has yet to publish its review into the matter (and did not respond to our requests for comment).
America may not always dominate the atmosphere. China, the European Union and others have plans for satellite mega-constellations of their own. China intends to launch at least three, which are together due to include some 38,000 satellites, and Europe’s IRIS constellation will have 290. Rwanda, an unlikely competitor, has filed a request for two constellations with more than 327,000 satellites. The EU and Rwanda are in the process of developing environmental regulations. China’s laws do not specify the need for environmental assessment; they do, however, require the space environment to be protected.
There may also be technical solutions. Satellites can be made smaller, even if that is not the current trend. Starlink’s spacecraft weigh about 800 kilograms at launch, and Elon Musk, SpaceX’s boss, predicts future generations will be even heavier. Some scientists have suggested alternative construction materials, such as carbon fibres or wood, which could reduce the need for exotic substances. Yet these may have negative consequences of their own. Wood, for instance, could incinerate upon being decommissioned, releasing lots of black soot into the atmosphere, which would trap heat and possibly darken the sky.
Another focus is a satellite’s final moments. “The dominant thinking about re-entry was that all of the material would stay in pieces large enough to just fall out of the atmosphere and not accumulate in the stratosphere,” says Martin Ross, of the Aerospace Corporation, an American firm. This has turned out to be wrong. Some researchers argue that the FCC needs to rethink its five-year rule and extend the lifetime of commercial satellites, in order to avoid the need for so many future launches. Others suggest mega-constellations could be shared between countries. As international tensions rise, however, that idea may turn out to be pie in the sky. ■
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