Energetic particle data recorded onboard Giotto during the first encounter of an observing spacecraft coming from deep space with Planet Earth
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The Giotto Spacecraft executed an Earth-Gravity-Assist manoeuvre on 2-3 July 1990 and two onboard scientific instruments, namely the energetic particle analyser (EPONA) and the magnetometer (MAG), were set into operation during the associated (33h) encounter. Contemporaneous data show that the magnetosphere was relatively undisturbed during this Earth Swingby so that the signatures recorded by EPONA effectively provide a "snapshot" of the quiet magnetosphere in energetic particles along a unique, hyperbolic, high-inclination orbit. Protons in the range ∼ 30-200 keV recorded in the region upstream of the bow shock are interpreted to have been accelerated, via the diffuse shock acceleration mechanism, at the (inbound) quasi-parallel bow shock. The temporal profiles of those proton and electron fluxes recorded near closest approach, where Giotto traversed part of the outer radiation belt, are compared with profiles generated using NASA's AP-8 MIN and AE-8 MIN programs to model parti cle fluxes along this segment of the trajectory. Characteristic features of the measured energetic proton and (MeV) electron fluxes are, thereby, shown to match the modelled signatures of trapped radiation in the (outer) Belt. The EPONA data provide no evidence of a midnight cusp source of energetic particles. Outbound, where magnetic records show that "flapping" of the magnetopause boundary was a feature, variations in the particle record reflect spacecraft traversals back and forth from the magnetosphere to the magnetosheath. It is inferred that proton fluxes in the range <30-> 200 keV identified between both the inbound and the outbound magnetopause and the bow shock comprise a sheath of (Fermi) accelerated protons enveloping the magnetosphere. The transit time damping mechanism is suggested to have contributed to producing the rather high fluxes (relative to the inbound pass) of energetic particles recorded downstream of the bow shock.
CitationMcKenna-Lawlor, S.; Kirsch, E.; Heynderickx, D.; Lemaire, J. (2001). Energetic particle data recorded onboard Giotto during the first encounter of an observing spacecraft coming from deep space with Planet Earth. , Planetary and Space Science, Vol. 49, Issue 13, 1365-1378, DOI: 10.1016/S0032-0633(01)00049-6.