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Sublimation from icy jets as a probe of the interstellar volatile content of comets


Comets are some of the most primitive bodies left over from the Solar System's early history. They may preserve both interstellar material and material from the proto-solar nebula, and so studies of their volatile components can provide clues about the evolution of gases and ices, as a collapsing molecular cloud transforms into a mature planetary system1,2. Previous observations of emission from rotational transitions in molecules have averaged over large areas of the inner coma, and therefore include both molecules that sublimed from the nucleus and those that result from subsequent chemical processes in the coma. Here we present high-resolution observations of emission from the molecules HNC, DCN and HDO associated with comet Hale–Bopp. Our data reveal arc-like structures—icy jets—offset from (but close to) the nucleus. The measured abundance ratios on 1–3″ scales are substantially different from those on larger scales3,4,5, and cannot be accounted for by models of chemical processes in the coma2,6,7; they are, however, similar to the values observed in the cores of dense interstellar clouds and young stellar objects. We therefore propose that sublimation from millimetre-sized icy grains ejected from the nucleus provides access to relatively unaltered volatiles. The D/H ratios inferred from our data suggest that, by mass, Hale–Bopp (and by inference the outer regions of the early solar nebula) consists of 15–40% of largely unprocessed interstellar material.

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Figure 1: Contour images of millimetre-wave rotational line emission from the coma of comet Hale–Bopp.
Figure 2: OVRO images of the DCN J = 3 → 2 (217.238 GHz) emission in the coma of Hale–Bopp.

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We thank the staff at OVRO and D. K. Yeomans at JPL for support of our Hale-Bopp observations. The OVRO Millimeter Array is operated by the California Institute of Technology under funding from the US NSF. M.R.H. was supported by the Miller Institute for Basic Research in Science. G.A.B. was a Visting Fellow at the University of Colorado; additional support to G.A.B. from the NASA Exobiology and Origins of Solar Systems programs is acknowledged.

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Correspondence to Geoffrey A. Blake.

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Blake, G., Qi, C., Hogerheijde, M. et al. Sublimation from icy jets as a probe of the interstellar volatile content of comets. Nature 398, 213–216 (1999).

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