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[5.02] The Abundance of Carbon Monoxide in Neptune's Atmosphere

B.E. Hesman (University of Saskatchewan), G.R. Davis (University of Saskatchewan/Joint Astronomy Centre), H.E. Matthews (DRAO/HIA, NRC Canada)

The unexpected discovery of carbon monoxide in the stratosphere of Neptune in 1991 has important implications for the origin of the planet. The two potential sources of CO in Neptune are infalling material from the interplanetary medium, and convection due to Neptune's internal heat source. The tropospheric CO abundance would be a key discriminator between these two possibilities.

The CO J=3-2 absorption line (345 GHz) is strongly pressure-broadened and is difficult to measure using high-resolution heterodyne spectroscopy. In 2003/04, 25 discrete segments across this line were measured using the heterodyne receiver B3 at the James Clerk Maxwell Telescope (JCMT). This high-resolution data set included both the stratospheric emission and the tropospheric absorption due to CO in Neptune's atmosphere, and has allowed a full CO profile to be determined. The current findings are a tropospheric abundance significantly less than in the stratosphere.

This research is supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.