CO ON TITAN - EVIDENCE FOR A WELL-MIXED VERTICAL PROFILE

We report on new microwave heterodyne observations of the CO J(1-0) ro tational transition from the stratosphere of Titan made in October 199 4 with the Owens Valley Radio Observatory millimeter array. The spectr um obtained clearly exhibits a strong emission core over the similar t o 600-MHz bandwidth of the upper sideband spectrometer. The lineshape, referenced to the flat spectrum simultaneously observed in the lower sideband, was inverted to determine a best fit CO mixing ratio profile consistent with the observations. The best fit profile is a constant mixing ratio of 5 +/- 1 x 10(-5) over the altitude range of 60-200 km. Combined with IR observations of tropospheric CO at 6 x 10(-5) (B. L. Lutz et al. 1983, Science 220, 1374-1375), this result provides stron g evidence that CO is well mixed from the surface to at least 200 km i n Titan's atmosphere. (C) 1995 Academic Press, Inc.