High early solar activity inferred from helium and neon excesses in the oldest meteorite inclusions

L. Kööp, P. R. Heck, H. Busemann, A. M. Davis, J. Greer, C. Maden, M. M. M. Meier & R. Wieler

Nature Astronomy (2018)
Published: 30 July 2018


“Astronomical observations show that early in their evolution, stars experience stages of high activity associated with enhanced energetic particle fluxes. The Sun’s early activity is often inferred from the spallogenic isotope record (for example, 10Be) in the Solar System’s oldest materials, calcium–aluminium-rich inclusions (CAIs) in meteorites. However, the 10Be record could be affected by processes other than in situ irradiation by solar particles. Noble gases can give less ambiguous insights because they are inert volatiles and hence not incorporated into CAIs during their formation. Here we show that hibonite-rich CAIs, considered to have formed before 26Al-rich CAIs, contain helium and neon excesses that can be unambiguously attributed to in situ irradiation by energetic particles. Given their volatile nature, we infer that the noble gases were produced by irradiation in a relatively cold region at a considerable distance from the Sun (not at the inner disk edge), requiring high particle fluxes and thus high early solar activity. Because more evolved CAIs lack comparable noble gas irradiation records, we conclude that the oldest Solar System materials experienced a phase of intense irradiation not recorded by materials that formed later. Consequently, disk properties or energetic particle fluxes changed significantly during the very early phases of Solar System evolution.”