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Nitrogen isotope abundances in the recent solar wind
1Department of Chemistry 0317, University of California, San Diego, La Jolla 92093-0317, USA.
Nature
|June 1, 1995
Summary
Lunar regolith contains nitrogen primarily from solar wind, not crystalline rocks. New measurements reveal this solar wind nitrogen has a higher 15N/14N ratio than Earth's atmosphere.
Area of Science:
- Lunar and Planetary Science
- Geochemistry
- Cosmochemistry
Background:
- Lunar crystalline rocks are nitrogen-poor, while regolith samples show significant nitrogen content (up to 0.012% by mass).
- Lunar regolith nitrogen correlates with noble gases implanted by solar radiation, suggesting a solar origin.
- Variations in the nitrogen isotope ratio (15N/14N) in regolith samples hint at long-term solar wind isotopic changes, but direct solar wind measurements are lacking.
Purpose of the Study:
- To determine the 15N/14N ratio of contemporary solar wind.
- To provide a reliable isotopic signature for nitrogen implanted in the lunar surface over the last 10^5 to 5x10^7 years.
Main Methods:
- Analysis of nitrogen isotopes in two lunar regolith samples with simple and recent exposure histories.
- Measurement of the 15N/14N ratio in the implanted nitrogen.
Main Results:
- Nitrogen implanted in the lunar surface over the past 10^5 to 5x10^7 years exhibits a 15N/14N ratio approximately 40% higher than that of the terrestrial atmosphere.
- This measured ratio is substantially lower than most prior estimations for the solar wind's isotopic composition.
Conclusions:
- The study provides a new, robust measurement of the 15N/14N ratio in the present-day solar wind.
- This finding helps to explain isotopic variations observed in lunar regolith and offers insights into the long-term evolution of solar composition.
Keywords:
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