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Long‐term compositional variation in solar corpuscular radiation: Evidence from nitrogen isotopes in the lunar regolith
Author(s) -
Kerridge John F.
Publication year - 1993
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/93rg01953
Subject(s) - regolith , noble gas , solar energetic particles , astrobiology , solar system , isotopes of nitrogen , population , range (aeronautics) , nitrogen , isotope , atmospheric sciences , physics , materials science , atomic physics , solar wind , coronal mass ejection , nuclear physics , plasma , demography , quantum mechanics , sociology , composite material
Implantation of solar corpuscular radiation into the lunar surface generates a population of solar atoms in the rims of lunar regolith grains. Laboratory analysis of those atoms can yield a measure of solar composition. Nitrogen trapped in the lunar regolith consists of at least two components, putatively originating in the Sun, differing in release temperature and therefore probably in implantation energy. The higher‐energy component is depleted in 15 N relative to the lower‐energy component by amounts that range up to at least 20%. These components superficially resemble those identified previously in the solar‐derived light noble gases, though with several marked differences. Thus the higher‐energy noble gas components are depleted in the lighter isotope. Unlike the noble gas case, the 15 N/ 14 N ratios of both N components vary with antiquity in a complex fashion; the lower‐energy component echoes the variations in the higher‐energy component which dominate the isotopic evolution of the bulk samples. The magnitude of the bulk sample variation exceeds 30%; the higher‐energy component varies by at least 25%. The bulk long‐term trend in 15 N/ 14 N does not result from variations in mixing ratio of the two components. Both the compositional difference between the components and the long‐term variations within them apparently originate in the Sun, though this conclusion is inconsistent with current understanding of solar structure and evolution. The nitrogen isotopic record therefore appears to represent a major challenge to solar physics.