Comets: Gas in the Inner Coma

Details Comets: Gas in the Inner Coma Comets: Gas in the Inner Coma

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003hst..prop.9985f&link_type=abstract

HST Proposal ID #9985

Computer Science

Hst Proposal Id #9985

Scientific paper

Our target of opportunity program aims at understanding the nucleus-coma interface in comets. Imaging of the near-nucleus region, from both the in situ spacecraft missions to comet Halley in 1986, and more recently with the WFPC2 Planetary Camera, has revealed the structure and evolution of the dust jets associated with active areas on the surface of the nucleus. These dust jets are thought to be driven by the vaporization of the volatiles trapped in the cometary ice. However, the total source inventory of the gaseous component of the coma is not known as there has not been to date direct imaging of a "parent" molecule vaporized directly from the nucleus. In the spectral range of the SBC, the dominant emissions are the Fourth Positive band system of CO and the resonance transitions of its dissociation products carbon and oxygen {oxygen is also produced by the photodissociation of water}. The latter, as dissociation products, are rather extended but the CO emission is concentrated close to the nucleus {McPhate et al. 1999}. Thus, imaging with the SBC using the BaF_2 filter to remove the OI 1304 A will provide a measure of the gas flow leaving the comet's nucleus. In the event of outbursts {often associated with the rotation of active areas into the sunlit hemisphere}, sequential images can provide a direct measure of the gas outflow velocity. The possible presence of a distributed source of CO {such as the purported "CHON" grains invoked to explain the distribution recorded by the Giotto neutral mass spectrometer at Halley} will also be determined. We note that while CO can be detected spectroscopically from the ground at both infrared and millimeter wavelengths, both of these require very high spectral resolving power and the techniques are not suitable for direct imaging of the CO.

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