Solar flare irradiation records in Antarctic meteorites

Abstract

Petrographical studies 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, 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 times. Relatively fewer Antarctic meteorites have been studied for their noble gas content and records of cosmic ray heavy nuclei tracks (ref. 14 and N. Bhandari, unpublished results); there has been no evidence of solar flare tracks and solar wind noble gases in the analysed samples.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.