Numerous satellite operators are building megaconstellations in Low Earth Orbit (LEO) with hundreds of satellites, placing new satellites and spent rocket stages in orbit. Once these objects fail, they are often removed from LEO via atmospheric reentry, producing metallic particles that can interact with ozone chemistry and Earth’s radiative balance. The extent of these interactions remains poorly understood despite their importance to current space governance and policymaking.
Helping to address this gap, this paper estimates the distribution, lifetime and direct radiative forcing of reentry-ablated alumina using an Earth system model. We consider a future scenario where all megaconstellations publicly filed at the Federal Communications Commission as of 2022 are operating, amounting to 2.52 Gg/yr of reentry-ablated alumina emissions.
As a conservative approximation, we find that reentry-ablated alumina particles have an atmospheric lifetime between one and two years, leading to a cooling radiative forcing of approximately -0.378mW/m2.
Simulations with fine alumina particles produce between 14% and 36% larger radiative forcings and have lifetimes 1.54 times longer than simulations with coarse alumina emissions.
Alumina emitted only in the South Pacific produces an asymmetrical radiative forcing.
Furthermore, modeling alumina with time-averaged, constant emissions rather than in discrete reentry plumes in results in 21% to 24% overestimation of alumina’s radiative forcing.
These results are sensitive to numerous assumptions on initial particle size, radiative indices and coagulation characteristics of the aerosol. In-situ observation and a sophisticated understanding of reentry-ablated alumina particles are necessary to better predict the atmospheric consequences of reentry-ablated alumina.