Millimeter Spectroscopy of Uranus and Neptune: Constraints on CO and PH 3 Tropospheric Abundances

Author： Encrenaz T. Serabyn E. Weisstein E.W.

ISSN： 0019-1035

Source： Icarus, Vol.124, Iss.2, 1996-12, pp. : 616-624

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Abstract

Spectra of Uranus and Neptune have been obtained in the 190-310 GHz frequency range (i.e., 6.3-10.3 cm -1 , wavelength range 1.0-1.5 mm), with a Fourier transform spectrometer at the Caltech Submillimeter Observatory. The data, with a spectral resolution of 7.2 GHz, were analyzed in a search for CO and PH 3 . Neither the CO (2-1) transition at 230 GHz nor the PH 3 (1-0) transition at 267 GHz were detected. The absence of a detectable absorption feature at the position of the CO (2-1) line favors a CO tropospheric mixing ratio lower than 5 x 10 -7 in Uranus and 1.0 x 10 -6 in Neptune (3sigma limits). In the case of Neptune, a tropospheric mixing ratio of 6 x 10 -7 seems to be in best agreement with all the existing low resolution data for CO. In the case of Uranus, a PH 3 enrichment by more than a factor of 4 can be excluded. There is no evidence for strong PH 3 supersaturation in either Uranus or Neptune.