Photoprocessing of H2S in interstellar grain mantles as an explanation for S2 in comets

Details Photoprocessing of H2S in interstellar grain mantles as an explanation for S2 in comets Photoprocessing of H2S in interstellar grain mantles as an explanation for S2 in comets

Jul 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987a%26a...181..155g&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 181, no. 1, July 1987, p. 155-168.

Astronomy and Astrophysics

Astrophysics

38

Cometary Atmospheres, Hydrogen Sulfide, Interstellar Matter, Photolysis, Sulfur, Absorption Spectra, Cosmic Dust, Emission Spectra, Ultraviolet Radiation, Comets, Sulfur, Hydrogen Sulfide, Mantles, Grains, Dust, Molecules, Spectroscopy, Ultraviolet, Wavelengths, Radiation, Laboratory Studies, Iras-Araki-Alcock, 1983Vii, Source, Origin, Analogs, Photolysis, Ice, Composition, Experiments, Formation, Temperature, Diffusion, Spectra, Procedure, Emissions, Fluorescence, Absorption, Calculations, Depth, Optical P

Scientific paper

The observation of S2 in comet IRAS-Araki-Alcock 1983 VII has raised critical questions regarding whether the precometary formation of this molecule occurred in the gas phase or in the solid interstellar ices. The implications of these results on the origin of comets are interpreted using laboratory analogue experiments on S2 formation. It is shown that ultraviolet photolysis of H2S embedded in dirty ices composed of molecules such as H2O, CO and CH4 converts the H2S molecules into S2 and other sulfur bearing species. From these experiments, using the cosmic abundance of sulfur relative to oxygen, it is calculated that the [S2]/[H2O] ratio in interstellar grains lies between 2×10-4 and 1.4×10-3, consistent with the observed ratio [S2]/[OH] = 5×10-4 in IRAS-Araki-Alcock 1983 VII. It is argued that S2 cannot be simply used as a discriminant for the comet formation temperature, unless one properly takes into account the aggregation time scales. The experiments suggest that for comet formation times of 106yr temperatures well under 100K are indeed required so that comets could have been formed no closer than the Uranus-Neptune region.

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