Lidar detects 10-fold lithium plume at 96 km traced to Falcon 9 re-entry
Feb 23rd 2026
A resonance fluorescence lidar in Kuehlungsborn recorded a transient 10-fold increase in mesospheric lithium about 20 hours after an uncontrolled Falcon 9 upper stage re-entry, with back trajectories linking the plume to the re-entry path west of Ireland.
- A resonance fluorescence lidar measured a 10-fold enhancement of atomic lithium between 94.5 and 96.8 km at 00:21 UTC on 20 February 2025 lasting about 40 minutes.
- Backwards trajectories computed with UA-ICON winds nudged to ECMWF and perturbed by radar-measured variability traced the sampled air to the Falcon 9 re-entry track at roughly 100 km altitude west of Ireland.
- Concurrent ionosonde, meteor radar, and geomagnetic data showed no strong sporadic E activity or geomagnetic disturbance that could plausibly explain the neutral lithium layer naturally.
- This is the first ground-based lidar observation attributed to upper-atmospheric pollution from a space debris re-entry and the first observational evidence that ablation can begin near 100 km altitude.
- The large disparity between natural meteoric lithium input and the lithium content of a single Falcon 9 upper stage makes lithium an effective tracer of anthropogenic re-entry emissions.
- The study demonstrates that identifying re-entry pollutants and tracing them to their sources is feasible and highlights the need for expanded monitoring as re-entry rates increase