Comets Halley, carbonate

FIGURE 13 Objective-grating far-UV spectrum of Comet Halley, obtained by the Naval Research Laboratory in a 1986 sounding rocket flight, which excludes the hydrogen Lyman a emission. The spectrum reveals far-UV emissions of atomic oxygen, carbon, sulfur, and also carbon monoxide (CO) (unlabeled features between the OI and CI features). 

Mineralogical interpretations of Halley dust analyses remain controversial. Lawler et al. (1989) saw no clustering of compositions that might suggest crystalline minerals (Fig. 12.5), whereas Fomenkova et al. (1992) identified compositions that were consistent with a number of minerals, including pyroxene, phyllosilicate, carbonate, FeNi metal, iron sulfide, and iron oxide. The characterization of minerals in returned comet dust (see below) supports the identification of some of these primary minerals but calls into question the identification of those formed by alteration. 

Evidence for carbynes in comets might come from remote-sensing analyses of the volatile species in the coma of active comets, in particular from the study of carbon-chain molecules abundances [88]. Using narrowband filter photometry, C3 and C2 were detected in amounts that are classified as being typical in comets Hale-Bopp and Halley [89] and as "being depleted in carbon-chain molecules in comet 67P/Churyumov-Gerasimenko, the new target of the ESA ROSETTA mission, and comet LINEAR 1999... 

PAHs comprise a large percentage of the carbon found in interstellar space. They have even been observed in interstellar ice (Halley s comet, for example). It has been shown that ultraviolet irradiation of PAHs in ice produces aromatic ketones (Chapter 9), alcohols (Chapter 7), and other compounds, suggesting a role of PAHs in prebiotic chemistry (see A Word about Methane, Marsh Gas, and Miller s Experiment, page 60). 

Ultraviolet observations of several comets, including West (1975) and Halley (1986) (Fig. 13), revealed that CO is also a prominent cometary constituent. Ultraviolet observations have also resulted in the detection of minor species not previously observed in comets, including atomic and diatomic sulfur, ionized carbon, and the SH radical. Future, more sensitive observations and ones extending to shorter wavelengths are expected to reveal other constituents, such as H2, N2, N, N+, and 0+. 

Reach, W.X, Rho, J. Detection of far-infrared water vapor, hydroxyl, and carbon monoxide emissions from the supernova Remnant 3C 391. Astrophys. J. Lett. 507, 93-97 (1998) Reinhard, R. Summary of the scientific results of the Giotto Mission to Halley s comet nucleus, dust and gas composition and fluxes. In Cometary and Solar Plasma Physics, p. 81 (1988)... 

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