Space junk returning to the Earth is introducing metal pollution to the pristine upper atmosphere as it burns up on re-entry, a new study has found.
Authors
- Robyn Schofield
Professor and Associate Dean (Environment and Sustainability in Faculty of Science), The University of Melbourne
- Robert George Ryan
Research Fellow in Atmospheric Composition, The University of Melbourne
Published today in the journal Communications Earth & Environment, the study was led by Robin Wing from the Leibniz Institute of Atmospheric Physics in Germany. Using highly sensitive lasers, he and his team of international researchers observed a plume of lithium pollution, tracking it back to the uncontrolled re-entry of a discarded Space X Falcon 9 rocket upper stage.
This is the first observational evidence that re-entering space debris leaves a detectable, human-caused chemical fingerprint in the upper atmosphere. This was also the first time a pollutant plume from a specific space junk re-entry event has been monitored from the ground.
With many more satellite launches planned for the future , this event won't be the last. It highlights the urgent need for governments and the space industry to tackle this problem before it gets out of hand.
A part of the atmosphere we barely understand
The region that comprises the upper stratosphere, mesosphere, and lower thermosphere (around 80 to 120 kilometres above Earth) is one of the least studied parts of the Earth system. It's too high for balloons, too low for satellites, and too harsh for aircraft.
Yet this region is crucial for radio and GPS communications, upper atmospheric weather patterns, and stratospheric ozone.
The upper atmosphere is largely unpolluted by humans. But the new space age is injecting growing quantities of metals and other pollutants from satellites, rocket bodies and space debris.
The impact this will have on the stratospheric ozone layer, which is crucial to protecting life on Earth from harmful ultraviolet radiation, is as yet unquantified. But early findings are cause for concern.
For example, research from 2024 suggests aluminium and chlorine emissions related to rocket launches and re-entries may slow the ozone layer's recovery.
Soot from rocket launches is also likely to cause warming in the upper atmosphere .
Finding lithium with lasers
For the new study, the researchers used a highly sensitive laser-based sensor to detect the fluorescence of trace metals in the mesosphere and lower thermosphere. This is not an off-the-shelf and readily available observation system, but it could be.
On February 20 2025, they captured a clear, sudden enhancement in lithium ions from lithium batteries and human-made metal casings used in satellites. These are quite distinct from natural meteor material.
Using atmospheric trajectory modelling, they traced the timing and altitude of the lithium plume directly to the re-entry path of a discarded Falcon 9 rocket stage as it burnt up through the lower thermosphere into the mesosphere over the Atlantic Ocean, west of Ireland.
A rapidly escalating problem
The number of satellites in orbit has exploded from a few thousand a couple years ago to roughly 14,000 right now , driven largely by megaconstellations.
There are many more satellites planned. In fact, SpaceX has applied to launch a megaconstellation of up to one million satellites to power data centres in space. Every one of these satellites will eventually re-enter the atmosphere. So too will the rockets that launch them.
Current estimates suggest that by 2030 , several tonnes of spacecraft material will burn up in the upper atmosphere every single day.
So far, there is no regulatory framework for these emissions, few monitoring options and limited scientific understanding of the likely impacts.
The new lithium detection demonstrates that pollutants from re-entry are measurable and can be traced back to individual re-entry events. This is an important step when it comes to holding companies involved in space accountable.
International regulatory bodies need to be set up to liaise with governments and scientists to establish monitoring networks and instruments to track changes to our atmosphere from this emerging threat.
As the space industry skyrockets, our efforts to understand, monitor and regulate upper-atmospheric emissions must keep pace.
Robyn Schofield receives funding from the Australian Research Council, Medical Research Future Fund, the Reef Restoration and Adaptation Program and Murujuga Rock Art Monitoring Program. She is an ACCESS-NRI board member, an expert advisory group member of The Safer Air Project, Australian Meteorological and Oceanographic Society expert chair of atmospheric and oceanographic composition and an Associate Investigator of the ARC Centre of Excellence for Weather of the 21st Century. From 2016-2024 she was also an elected member of the International Ozone Commission.
Robert George Ryan receives funding from the Reef Restoration and Adaptation Program and Murujuga Rock Art Monitoring Program. He has also received funding from the European Research Council to research upper tropospheric chemistry. He is an early career researcher member of the Australian Meteorological and Oceanographic Society (AMOS).
