The Sun Reflected in Osbornite

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Science  09 Mar 2007:
Vol. 315, Issue 5817, pp. 1339-1341
DOI: 10.1126/science.315.5817.1339d

Knowing the chemical composition of the solar nebula is critical for understanding how the Sun and planets condensed from a cloud of gas, and for making benchmark comparisons as solar system materials are reprocessed in the solar wind and planetary atmospheres. However, although the Sun contains 99.8% of the mass in the solar system, its composition remains unclear.

Meibom et al. argue that analysis of a rare mineral in a meteorite has allowed accurate inference of solar nebula nitrogen and carbon isotope ratios. A speck of osbornite (TiN bearing some trapped TiC) was spotted in a calcium-aluminum-rich inclusion within the carbonaceous chondrite meteorite Isheyevo, which has been little altered since its formation. The osbornite is produced at very high temperatures (∼2000 K), so must have formed by gas-to-solid condensation in the solar nebula without changes in the isotopic composition. As supporting evidence, the measured 13C/12C ratio of 0.01125 ± 0.00008 (1σ) is consistent with the isotope ratio of carbon in the solar photosphere, and the 15N/14N ratio of (2.356 ± 0.018) × 10−3 matches the nitrogen composition in Jupiter's atmosphere and in the interstellar medium. — JB

Astrophys. J. 656, L33 (2007).

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