The Earth atmosphere-like bulk nitrogen isotope composition obtained by stepwise combustion analyses of Ryugu return samples
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2024-08
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Journal Article
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Abstract
The nitrogen isotope compositions of two samples returned from the asteroid Ryugu were determined using a stepwise combustion method, along with Ivuna (CI) and Y-980115, a CI-like Antarctic meteorite, as references. The two Ryugu samples A0105-07 and C0106-07 showed bulk delta 15N values of +1.7 +/- 0.5 parts per thousand and +0.2 +/- 0.6 parts per thousand, respectively, significantly lower than Ivuna with +36.4 +/- 0.4 parts per thousand, but close to Y-980115 with +4.0 +/- 0.3 parts per thousand. The Ryugu samples are further characterized by C/N and 36Ar/N ratios up to 3.4x and 4.9x the value of Ivuna, respectively. Among all Ryugu samples and CI chondrites, a positive correlation was observed between nitrogen concentrations and delta 15N values, with samples with lower nitrogen concentrations exhibiting lower delta 15N. This trend is explained by a two-component mixing model. One component is present at a constant abundance among all CI-related samples, with a delta 15N value around 0 parts per thousand or lower. The other varies in abundance between different samples, and exhibits a delta 15N value of +56 +/- 4 parts per thousand. The first 15N-poor endmember is seemingly tightly incorporated into a carbonaceous host phase, whereas the 15N-rich endmember can be mobilized and decoupled from carbon, potentially because it is in the form of ammonia. Asteroid materials with volatile compositions that are similar to those reported here for the Ryugu samples are attractive candidates for the volatile sources among Earth's building blocks.
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59 (8)
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2117 - 2133
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Wiley
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03956 - Vance, Derek / Vance, Derek
03946 - Schönbächler, Maria / Schönbächler, Maria