This article describes the first direct detection of atmospheric pollution caused by the re-entry of space debris. The case occurred following the uncontrolled re-entry of a Falcon 9 rocket upper stage in February 2025. Approximately 20 hours after the event, a scientific laser (a lidar) located in Germany detected a cloud of lithium atoms at an altitude of 96 km, a region of the atmosphere where there are normally negligible amounts of this element. In fact, the concentration observed was ten times higher than usual.

The researchers reconstructed the trajectory of that air mass using atmospheric models and wind measurements. The result: it coincided with the rocket's route after traveling about 1,600 km from the Atlantic. In addition, they ruled out that this lithium-rich air mass was related to any natural phenomenon, such as geomagnetic storms or known ionospheric processes.

Lithium is a key element in this research because it rarely reaches the upper layers of the atmosphere naturally from meteorites, but it is present in materials that form part of rockets and artificial satellites. Therefore, detecting it acts as a ‘chemical signature’ of human origin.

This study demonstrates for the first time that the disintegration of spacecraft leaves measurable traces in the upper layers of the atmosphere, that this disintegration begins at an altitude of around 100 km, and that we can trace this pollution back to its source. This is highly relevant, as we are entering an era of satellite megaconstellations. This means that thousands of objects will re-enter the atmosphere each year, injecting metals into atmospheric layers that influence ozone, aerosols, and the planet's radiative balance. We do not yet know the total impact, but thanks to this study, we do know that the phenomenon is real and quantifiable. However, the results suggest that it would be advisable to have a network of lidar detectors similar to those used in this work to better quantify the effect of this type of pollution on the atmosphere.

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