Satellite space junk can wreak havoc in the stratosphere

Earth’s space junk may be wreaking havoc in the stratosphere.

The rapid growth of satellite megaconstellations is connecting much of the world to broadband Internet. But every year, hundreds of those satellites die, burning up in the atmosphere as they fall. And every year, more and more satellites are being launched to replace them.

Dying satellites, it turns out, don’t just wink at the ether. Everyone leaves behind a little bit of themselves.

The fiery death of satellites, along with a huge increase in the number of rocket launches, is adding a huge amount of ozone-depleting and climate-changing pollutants to the stratosphere, researchers say. What this means for the planet’s atmospheric chemistry – including the ozone layer that protects against ultraviolet light – is not yet clear. But scientists are racing to find out.

“Launches are increasing so quickly,” says Daniel Murphy, an atmospheric scientist at the National Oceanographic and Atmospheric Administration’s Chemical Sciences Laboratory in Boulder, Colo. “In the last two years, there have been roughly 500 reentry events a year. , and people are talking about 10,000 in the not-too-distant future. That’s about one per hour. So we want to understand the implications as soon as possible.” be possible.”

Trade constellations

Currently, there are about 10,000 active satellites in orbit around the planet. Two-thirds belong to Starlink, SpaceX’s megaconstellation (SN: 3/3/23). Another 630 are part of London-based Eutelsat OneWeb. And other Internet projects aim to catch up quickly: In August, China launched the first 18 satellites for its Qianfan, or “Thousand Sails” constellation, eventually planned to include at least 12,000 satellites. Another planned Chinese project, known as Honghu-3, aims to link up to 10,000 satellites.

By some estimates, there could be as many as 100,000 satellites in near-Earth orbit by the 2030s, with perhaps half a million orbiting the planet in the decades to come.

These Internet satellites are disposable by design: They can serve for several years in a constellation network before they “decommission”—sink into a lower orbit until they eventually fall to a fiery death in the sky. Each disintegrating satellite injects metals into the atmosphere, many of which are metals that are either not normally found there or added in much greater amounts than are naturally introduced.

Narrative traces

The first step to understanding the extent of the problem is to identify the tracks of the burned spacecraft and whether those tracks are comparable or even detectable against the background of natural meteorite debris from space.

This research has just begun.

In 2023, Murphy and colleagues presented definitive evidence that metals specifically from spacecraft, rather than natural sources, were indeed high in the stratosphere, the layer of the atmosphere that extends from six to 20 kilometers above the Earth’s surface. Stratospheric sulfuric acid particles in the upper atmosphere above the Arctic were found to contain over 20 different elements consistent with spacecraft production. These elements, Murphy says, included niobium and hafnium, both refined from mineral ores for use in heat-resistant alloys. Other metals such as lithium, lead, aluminum and copper – which may be naturally present – were found in far greater abundance than can be spread organically through cosmic dust.

And evidence of past spaceships is piling up. From 2020 to 2022, scientists tracked a stratospheric increase in pollutants, corresponding to a rapid increase in satellite launches.

Emissions of aluminum and nitrogen oxides from satellite reentries nearly doubled from 3.3 billion grams in 2020 to 5.6 billion grams in 2022, atmospheric chemist Connor Barker of University College London and colleagues reported in April in Vienna at a meeting of the European Geophysical Union. By 2022, reentry inputs of nitrogen oxides, they found, were equivalent to about one-third of natural inputs of gases from meteorites. And alumina inputs were outpacing natural inputs by a factor of seven.

Pollutant emissions from rocket launches are also on the rise, Barker and his colleagues found. Fuel consumption nearly doubled from 2020 to 2022, from 38 billion grams to 67 billion grams. These release emissions can include pollutants such as black carbon, nitrogen oxides, carbon monoxide, aluminum oxide, and a variety of chlorine gases.

Chemical influences

Spacecraft debris can have a number of ripple effects through stratospheric chemistry.

It could spell bad news for the ozone layer in particular. Aluminum oxide, for example, is a byproduct of oxidation during the re-entry of aluminum-based spacecraft components, says José Ferreira, an aerospace engineer at the University of Southern California in Los Angeles. “And we know that aluminum oxides are catalysts for ozone depletion.”

This new threat to the ozone layer is particularly disappointing in the wake of the success of the Montreal Protocol, a 1987 agreement to ban the production and emissions of known ozone-depleting chemicals (SN: 2/10/21). By 2016, the annual hole in the ozone layer that forms over Antarctica was already showing signs of healing, on track to close completely within about 50 years (SN: 14.12.16).

There are a host of other ways that spacecraft pollutants can interfere with the atmosphere’s complex chemistry, Murphy says. Soot emitted by rocket engines absorbs solar energy, which can heat the atmosphere. Copper and other metals released during the burning of spacecraft wiring and connections are known to be powerful catalysts for chemical reactions in the atmosphere. Among other things, these metals can promote the creation of small particles that act as cloud seeds.

There is not much direct information about which of these reactions may already occur. The data that do exist are intended for computer simulations that track the life cycle of these pollutants and their interactions in the atmosphere. Murpyh’s team is planning more flights in 2025 to continue tracking the growing inventory of spacecraft debris.

Ferreira, meanwhile, is considering ways to incorporate an environmental impact assessment into the design phase of space missions. “If we identify in advance that a component or a chemical will be harmful to the atmosphere, we can find an alternative or invest in research into more environmentally friendly options,” says Ferreira.

Right now, the issue of impacts from scattered satellite materials is so new that there hasn’t been much funding to address it yet, Murphy says. But, he adds, “I think it has to happen quickly. It would be really nice to know these things before these satellites are built and launched.”