Refined composition of Solar Wind xenon delivered by Genesis NASA mission: Comparison with xenon captured by extraterrestrial regolith soils

Abstract

The Genesis mission captured Solar Wind (SW) and delivered it to Earth for laboratory analyses. Due to advanced mass spectrometric techniques developed specifically for analyses of returned Genesis SW-collectors, SW-oxygen, nitrogen and noble gas isotopes have been successfully measured providing new insights for cosmo- and geochemistry. SW-Xe collected by Genesis is the heaviest and the least abundant SW element analyzed. Here we describe in detail the experimental improvements we made over last 5 years and a latest refined SW-Xe isotopic composition. Combined with earlier, already published SW-Xe analyses, our new results provide the best current estimate for SW-Xe collected by Genesis: ¹³⁶Xe/¹³⁰Xe = 1.818 ± 0.004; ¹³⁴Xe/¹³⁰Xe = 2.242 ± 0.005; ¹³²Xe/¹³⁰Xe = 6.063 ± 0.010; ¹³¹Xe/¹³⁰Xe = 5.010 ± 0.012; ¹²⁹Xe/¹³⁰Xe = 6.314 ± 0.013; ¹²⁸Xe/¹³⁰Xe = 0.510 ± 0.001; ¹²⁶Xe/¹³⁰Xe = 0.0256 ± 0.0004; ¹²⁴Xe/¹³⁰Xe = 0.0292 ± 0.0004 (all errors are 1σ). The achieved precision allows resolving small, but now statistically significant isotopic difference between solar wind Xe and Xe trapped in lunar regolith samples. This emerging difference, not apparent prior to this study, likely points to the composition of indigenous lunar Xe and to the temporal evolution of terrestrial Xe. Combining our Xe fluence with that for other high first ionization potential (FIP) elements, we find that the depletion of elements with the FIP greater than 12 eV is not constant but monotonically decreases as FIP increases.