A 30-second exposure showing a Falcon 9 upper stage re-entering the atmosphere over Berlin, Germany, on February 19, 2025
Gerd Baumgarten
A SpaceX rocket that burned up after re-entering the atmosphere released a plume of vaporized metals over Europa, a type of pollution expected to increase as spacecraft and satellites proliferate.
The upper stage of a Falcon 9, which is designed to splash into the Pacific Ocean for possible reuse, lost control due to engine failure and fell from orbit over the North Atlantic in February 2025.
People across Europe saw burning debris streaking through the sky, some of which crashed behind a warehouse in Poland. Seeing the news, Robin Wing of the Leibniz Institute of Atmospheric Physics in Germany and his colleagues turned to lidar, an instrument for atmospheric sensing. Twenty hours later, it detected a 10-fold spike in lithium, a key component of rocket hulls, in the upper atmosphere as the plume of vaporized metal drifted above it.
Atmospheric modeling suggested that this cloud had drifted 1,600 kilometers from the area where Falcon 9 re-entered the atmosphere. The study is the first to trace high-altitude contamination to a specific spacecraft that has re-entered.
The tiny metal particles “can catalyze ozone depletion, create clouds in the stratosphere and mesosphere, and affect the way sunlight moves through the atmosphere,” says Wing. “But all of this is understudied.”
Concerns about this type of pollution are growing as commercial space launches take off and companies expand their mega-constellations of satellites, such as SpaceX’s Starlink and Amazon’s Leo. About 14,500 satellites are already in orbit, and last month SpaceX applied to launch 1 million more for Elon Musk’s goal of creating orbital data centers to power artificial intelligence.
To avoid a continuous cycle of collisions that produce ever more space debris, satellites are usually allowed to crash and burn up at the end of their lives. Experts say the amount of space debris particles could grow 50-fold over the next decade and exceed 40 percent of the mass currently brought into the atmosphere by meteoroids.
It is a misconception that space debris burns up in the atmosphere and disappears, says Daniel Cziczo of Purdue University, Indiana, who was not involved in the study. “Let’s hit the brakes here, and let’s really do a thorough analysis of what effect this material might have.”
The Falcon 9 feather contained an estimated 30 kilograms of lithium. But given the composition of the alloys in rocket hulls, it would have contained a far greater amount of aluminium.
Vaporized aluminum reacts with atmospheric oxygen to form particles of aluminum oxide, which provide a surface where chlorine compounds can more easily break down. The chlorine radicals released by this process react with and destroy ozone molecules in the stratosphere.
Scientists estimate that spacecraft burnouts release 1,000 tons of aluminum oxide into the atmosphere each year and counting. This threatens to widen the ozone hole in the Southern Hemisphere, which has been shrinking as countries phase out ozone-depleting refrigerant gases. The loss of ozone can let in more of the sun’s ultraviolet rays, which cause skin cancer.
“When it comes to metals, we’re kind of moving into this new paradigm where the upper atmosphere is increasingly affected by anthropogenic pollution rather than natural sources,” says Eloise Marais of University College London. “Space Debris Begins to Undo Ozone Hole Progress.”
The metal oxide particles can also serve as nuclei upon which water vapor can condense into droplets and form cirrus clouds in the upper troposphere, which tend to trap heat.
Scientists have measured particles from burnt-up spacecraft in cirrus clouds. If they encourage the formation of cirrus clouds, it could exacerbate global warming, although this effect would still be small compared to greenhouse gases such as carbon dioxide.
“There is a lot of scientific evidence that this material can have harmful effects on our atmosphere, and now it’s up to us as scientists to find out if these effects are taking place and how bad they are,” says Cziczo.
There may be solutions, such as building satellites out of materials such as wood – although that could still release black carbon soot on re-entry – or pulling more of them back into high-altitude ‘graveyard orbits’.
“We have to take some time and think about what we’re doing before we do it,” says Wing. “This explosion of satellites … it’s very fast and we don’t know the consequences.”
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