Evidence in meteorites for an active early sun

Abstract

High-sensitivity noble gas mass-spectrometric analyses of meteorite grains having solar flare heavy ion tracks show large enrichments of spallation-produced Ne-21 and Ar-38 when compared to nonirradiated grains from the same meteorite. The enhanced spallation effects in the irradiated grains are due to irradiation by energetic protons early in the history of the solar system, before compaction of the host meteorite. They require a proton fluence (E greater than 10 MeV) of 10 to the 16th to 10 to the 18th/cu cm. These results are best explained by solar flare irradiation in the early solar system with a proton flux several orders of magnitude higher than contemporary solar flares. The Ne isotopic structure suggests a harder energy spectrum than is characteristic of contemporary flares. These observations provide direct evidence for an active early (T Tauri) sun.