Self‐Limiting of Artificial Electron Radiation Belts: Evidence From the Starfish Prime High‐Altitude Nuclear Explosion

Abstract

The 1962 Starfish Prime high‐altitude 1.4‐megaton nuclear detonation injected large amounts of fission‐produced energetic electrons into the inner magnetosphere ( L  = 1.12), creating an intense artificial radiation belt that persisted for years. In this study, we revisit historical data from this unprecedented event to investigate the potential role of Kennel‐Petschek (K‐P) self‐limiting processes in capping the electron radiation fluxes arising from a nuclear explosion. Using digitized data from the Injun and STARAD satellites, we reconstruct an estimate for the spectral, spatial, and temporal evolution of the Starfish‐related electron flux. We show that by the time of the earliest global satellite measurements (∼10 hr post‐detonation), the flux spectrum appears to potentially be capped at levels consistent with the theoretical K‐P limit for energies below ∼2 MeV. We also attempt to place these observations in the context of the burst timeline: ground‐based measurements of immediately occurring broadband whistlers were likely associated with the initial electromagnetic pulse, whereas the later evolution of trapped particles over several hours could have been dominated by K‐P pitch angle scattering from a newly created trapped electron population. Acting alongside longitudinal drift equilibration and very slow Coulomb scattering on atmospheric neutrals, these processes could have reduced the excess energetic electron population until the trapped distribution approached marginal stability at the K‐P flux limit. Our results provide evidence that suggests that the intensity of the artificial radiation belts could be constrained by naturally occurring K‐P‐like self‐limiting plasma processes, resulting in the creation of an upper limit to even artificially create trapped electron space radiation.