A New Look at Neon-C and SEP-Neon

Abstract

Studies of the isotopic composition of neon in lunar soils, meteorites, and interplanetary dust particles have revealed several distinct components. In addition to implanted solar wind, which has a ^(20)Ne/^(22)Ne-abundance ratio of 13.7, there is an additional component with ^(20)Ne/^(22)Ne≈11.2, originally attributed to higher-energy solar energetic particles. Using data from the Advanced Composition Explorer, we have measured the fluence of solar wind, suprathermal particles, solar energetic particles and cosmic rays from ~0.3 keV/nucleon to ~300 MeV/nucleon over an extended time period. We use these measured spectra to simulate the present-day depth distribution of Ne isotopes implanted in the lunar soil. We find that the suprathermal tail of the solar wind, extending from a few keV/nucleon to several MeV/nucleon with a power law spectrum, can produce ^(20)Ne/^(22)Ne abundance ratios in the lunar soil that are similar to the measured composition, although there remain significant questions about the extent to which the present-day intensity of suprathermal ions is sufficient to explain the lunar observations.