Solar Wind and Spallation Neon in Small Dark Fragments Separated from the Kapoeta Howardite: Evidence for Early GCR Irradiation?

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The Kapoeta howardite contains abundant noble gases in the dark phases of its brecciated structure, implanted during exposure of the parent body regolith to the solar wind. These gases have been studied extensively over the years, most recently by the modern closed-system stepped etching technique, in efforts to determine the elemental and isotopic composition of the solar wind at the time of regolith exposure. Kapoeta is interesting as well for another aspect of its irradiation history: several investigations, most recently by Rao et al., have shown that the dark, solar-wind-irradiated phases contain excesses of spallation-produced Ne above the levels expected to be generated by galactic cosmic rays (GCR) during the meteorite's space exposure age of ~3 Ma. These excesses have been attributed to production by GCR, and by a solar cosmic ray (SCR) flux substantially enhanced over current levels, during an early ~3-6 Ma irradiation of the parent-body regolith prior to compaction, burial, and ultimate ejection of the Kapoeta object to space.


Physics and Astronomy