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Compositional homogeneity in the fragmented comet 73P/Schwassmann–Wachmann 3


The remarkable compositional diversity of volatile ices within comets1,2,3 can plausibly be attributed to several factors, including differences in the chemical, thermal and radiation environments in comet-forming regions, chemical evolution during their long storage in reservoirs far from the Sun4, and thermal processing by the Sun after removal from these reservoirs. To determine the relevance of these factors, measurements of the chemistry as a function of depth in cometary nuclei are critical. Fragmenting comets expose formerly buried material, but observational constraints have in the past limited the ability to assess the importance of formative conditions and the effects of evolutionary processes on measured composition5,6,7,8. Here we report the chemical composition of two distinct fragments of 73P/Schwassmann–Wachmann 3. The fragments are remarkably similar in composition, in marked contrast to the chemical diversity within the overall comet population and contrary to the expectation that short-period comets should show strong compositional variation with depth in the nucleus owing to evolutionary processing from numerous close passages to the Sun. Comet 73P/Schwassmann–Wachmann 3 is also depleted in the most volatile ices compared to other comets, suggesting that the depleted carbon-chain chemistry seen in some comets from the Kuiper belt reservoir is primordial and not evolutionary1.

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Figure 1: NIRSPEC spectra of the B and C fragments of comet 73P/Schwassmann–Wachmann 3.
Figure 2: Relative abundances of detected species in 73P/Schwassmann–Wachmann 3 and comparison to other comets.


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The NASA Planetary Atmospheres and Planetary Astronomy Programs supported this work. Data were obtained at the NASA IRTF operated by the University of Hawaii under cooperative agreement with the NASA Science Mission Directorate, Planetary Astronomy Program. Data were also obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. The Observatory was made possible by the financial support of the W. M. Keck Foundation. We acknowledge the assistance and expertise of B. Golisch, P. Sears, D. Griep, G. Hill and G. Puniwai, who helped to successfully obtain these data under difficult conditions; and we acknowledge that the summit of Mauna Kea, from which we had the privilege of conducting these observations, is revered within the indigenous Hawaiian community.

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Correspondence to N. Dello Russo.

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This file contains Supplementary Discussion, Supplementary Tables S1 -S2, Supplementary Figures S1-S3 with Legends and additional references. (PDF 1732 kb)

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Russo, N., Vervack, R., Weaver, H. et al. Compositional homogeneity in the fragmented comet 73P/Schwassmann–Wachmann 3. Nature 448, 172–175 (2007).

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