Journal Article

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

Bockelée-Morvan, D., Biver, N., Lisse, C. M., Russo, N. Dello, Vervack, R. J., Crovisier, J., Weaver, H. A.

2007

Overview

Comet 73P in pieces The 2006 visit of comet 73P/Schwassmann-Wachmann 3 (comet 73P) took it quite close to Earth. It had split a decade earlier into at least five fragments and by 2006, more than 60 fragments were orbiting the Sun. The comet's disruption had exposed fresh material that had been formerly buried deep within the comet's original nucleus. This provided ideal conditions for a natural equivalent to NASA's Deep Impact mission, digging even deeper into the comet than the probe that struck comet Tempel 1. Observation of fragments B and C of comet 73P showed them to be remarkably similar in composition. This contrasts to the marked variation in composition between different comets, and contradicts previous assumptions that short-period comets would have strong compositional variation with depth. A report of the chemical composition of two distinct fragments of comet 73P/Schwassmann–Wachmann 3. The fragments are similar in composition, in contrast to the chemical diversity of comets and contrary to the expectation that short-period comets should show strong compositional variation with depth. The remarkable compositional diversity of volatile ices within comets 1 , 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 Sun 4 , 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 composition 5 , 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 evolutionary 1 .

• Publisher: Nature Publishing Group UK,Nature Publishing,Nature Publishing Group
• Subject: Astronomy / Astrophysics / Chemical composition / Chemistry / Comets / Depletion / Earth, ocean, space / Evolutionary / Exact sciences and technology / Fragmentation / Fragments / Homogeneity / Humanities and Social Sciences / Ice / Interplanetary space / Kuiper Belt / letter / multidisciplinary / Nucleosynthesis / Observations / Physics / Reservoirs / Science / Solar system / Sun