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Solar Composition of Icy Planetesimals: A New Source For Comet Nuclei?
Published online by Cambridge University Press: 30 March 2016
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The enrichment of heavy elements on Jupiter appears to require the existence of a new class of icy planetesimal that exhibits solar relative abundances.
Prior to the Galileo probe mission, observations of methane in Jupiter’s atmosphere had revealed that C/H was approximately three times the solar ratio. This enrichment was thought to be the result of the delivery of heavy elements by icy planetesimals, which were assumed to be essentially identical to comets. However, comets are notoriously deficient in nitrogen (e.g., Geiss 1987; Krankowsky 1991) and recent upper limits on argon in three comets (Weaver et al. 2002) indicate that this element is also sub-solar relative to O. Hence it was assumed that Jupiter would exhibit the same deficiency in argon and nitrogen relative to carbon (Pollack and Bodenheimer 1989; Owen & Bar-Nun 1995). Yet the mass spectrometer on the Galileo Probe clearly showed that Ar, Kr, Xe, N, C, and S are all enriched in Jupiter’s atmosphere by the same factor of 3 ± 1 (Niemann et al. 1998; Owen et al. 1999).
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