Publication Date:
2016-01-15
Description:
Observations of the green and red-doublet emission lines have previously been realized for several comets. We present here a chemistry-emission coupled model to study the production and loss mechanisms of the O( 1 S) and O( 1 D) states, which are responsible for the emission lines of interest, for comet 67P/Churyumov-Gerasimenko. The recent discovery of O 2 in significant abundance relative to water (3.7±1.5 %) within the coma of 67P has been taken into consideration for the first time in such models. We evaluate the effect of the presence of O 2 on the green to red-doublet emission intensity ratio, which is traditionally used to assess the CO 2 abundance within cometary atmospheres. Model simulations, solving the continuity equation with transport, show that not taking O 2 into account leads to an underestimation of the CO 2 abundance within 67P, with a relative error of about 25 %. This strongly suggests that the green to red-doublet emission intensity ratio alone is not a proper tool for determining the CO 2 abundance, as previously suggested. Indeed, there is no compelling reason why O 2 would not be a common cometary volatile, making revision of earlier assessments regarding the CO 2 abundance in cometary atmospheres necessary. The large uncertainties of the CO 2 photodissociation cross section imply that more studies are required in order to better constrain the O( 1 S) and O( 1 D) production through this mechanism. Space weather phenomena, such as powerful solar flares, could be used as tools for doing so, providing additional information on a good estimation of the O 2 abundance within cometary atmospheres.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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