Space Debris Demise upon Re-entry as a Potential Atmospheric Pollutant

The number of orbiting bodies has increased significantly in an unrestricted and unregulated manner over the last decades, threatening sustainable access to space in the future. Ongoing plans to build mega-constellations of microsatellites will inevitably exacerbate this trend, adding to the ever-growing number of pieces of debris. Re-entry rates are expected to continue growing as the number of orbiting bodies increases while more satellites and launch vehicles remain in orbit. While it is widely understood that most objects will completely burn during re-entry, the effect of space debris demise on Earth’s atmosphere has only been lightly studied, and the long-term impact remains unknown. We resort to Reactive Molecular Dynamics simulations to resolve the oxidation process of the key structural material of aluminum for mesospheric re-entry, herewith presenting a first-order estimation of putative pollutant contributions from anthropogenic sources based on results from large-scale supercomputer runs on the generation of aluminum oxide nanoparticles. As of 2022, the total mass of re-entering objects from Low-Earth Orbit summed up to 309 metric tons, which consists of an 87 % increase in the yearly mass rate of aluminum injected at the top of the atmosphere compared to natural sources. Results show that aluminum oxides from space debris demise in the mesosphere amounted to 49 metric tons. These tend to cluster into nanoparticles, taking decades to decay into the stratosphere, where they may act as an ozone depletor.