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Decrease of the solar flare/solar wind flux ratio in the past several aeons deduced from solar neon and tracks in lunar soil plagioclases

1983; American Geophysical Union; Volume: 88; Issue: S02 Linguagem: Inglês

10.1029/jb088is02p0a713

2156-2202

R. Wieler, P. Etique, P. Signer, Gérard Poupeau,

Space Science and Extraterrestrial Life

We determined the He, Ne, and Ar concentrations and isotopic compositions of mineral separates of six lunar subsurface samples and of two regolith breccias which were exposed to the sun as early as 2–3 b. y. ago. The results are compared with our noble gas data obtained previously on mineral separates of lunar surface soil samples most of which contain recently implanted solar gases. The mean solar flare track densities were determined on aliquots of several of the plagioclase separates analyzed for noble gases. Solar wind retentive mafic minerals and ilmenites show that a possible secular increase of the 20 Ne/ 22 Ne ratio in the solar wind during the last 2–3 Ga is <2%. In plagioclases, which are less retentive for solar wind Ne, a considerable fraction of the retained Ne is of solar flare origin. The data are compatible with values for 20 Ne/ 22 Ne of ∼11.3–11.8, reported for solar flare Ne retained in plagioclase separates from lunar soils. The solar flare track data and the Ne data independently show that plagioclases exposed to the sun over the last 10 8 years recorded a lower mean ratio of solar flare to solar wind intensities than samples exposed about 1–3 b.y. ago. On the basis of track data we estimate these ratios to differ by a factor ∼2.