• Verchovsky, Alexander
• Anand, Mahesh
• Mortimer, James

Abstract

Simultaneous static-mode mass spectrometric measurements of nitrogen, carbon, helium, neon, and argon, extracted from the same aliquot of sample by high-resolution stepped combustion, have been made for a suite of five lunar soils.<br></br>Noble gas isotope ratios show that the majority of noble gases are derived from a solar wind source; for example, at peak release temperatures of 500–600 °C,²¹Ne/²²Ne = 0.0313 ± 0.0007 to 0.0333 ± 0.0007, and ²⁰Ne/²²Ne = 11.48 ± 0.05 to 12.43 ± 0.07, with values at the lowest temperature steps less fractionated during implantation from, and therefore even closer to, solar values (²¹Ne/²²Ne_SW = 0.03361 ± 0.00018 and ²⁰Ne/²²Ne_SW = 14.001 ± 0.042 (Pepin et al., 2012)). Despite the co-release of nitrogen and solar wind argon, measured nitrogen isotopic signatures at each temperature step, whilst variable, are significantly more enriched in ¹⁵N compared to the measured solar wind nitrogen value from the Genesis mission. Therefore, mixing between a ¹⁵N-enriched non-solar planetary nitrogen source with solar wind nitrogen is required to explain the measured isotopic values from the stepped combustion analysis of lunar soils. Binary mixing calculations, made under different assumptions about the degree of loss of solar wind ³⁶Ar, reveal that the majority (up to 98%) of the nitrogen released is derived from a non-solar source. The range of modelled non-solar end-member nitrogen compositions required to satisfy the measuredδ¹⁵N values varies between samples and temperature steps from +5‰ up to +300‰, or between +87‰ and +160‰ for bulk samples. This range of modelled isotopic compositions for the non-solar source of nitrogen encompasses measured values for several different groups of carbonaceous chondrite, as well as IDPs.

Topics

• impedance spectroscopy
• Carbon
• laser emission spectroscopy
• Nitrogen
• combustion