Solar flare irradiation records in Antarctic meteorites

Abstract

Petrographical studies^1,2 indicate that most meteorites collected from the Antarctic ice sheets are L and H chondrites of different metamorphic groups. Achondrites and iron meteorites constitute <5% of the total collection of about 1,600. Radio-nuclide^3–9, specifically ⁵³Mn, studies have suggested a multiple exposure history for some of the meteorites involving shielded exposure to cosmic rays either in large asteroidal-size parent bodies, from which the meteorites were ejected, or in relatively smaller-size objects that broke up in space in recent times³. Relatively fewer Antarctic meteorites have been studied for their noble gas content^10–13 and records of cosmic ray heavy nuclei tracks (ref. 14 and N. Bhandari, unpublished results); there has been no evidence of solar flare tracks and solar wind noble gases in the analysed samples. I now report the first observation of solar flare heavy nuclei tracks in Antarctic meteorite samples. Two interior specimens of sample 77216, an L-3 chondrite, contain track-rich grains indicating their exposure to solar flare irradiation before compaction of this meteorite. Preliminary noble gas data also indicate the presence of solar-type gases. Results of nuclear track studies of other Antarctic meteorite samples are presented.