Evidence for high-altitude haze thickening on the dark side of Venus from 10-micron heterodyne spectroscopy of CO2

Abstract

The 10.86- μ m P (44) and 10.33- μ m R (8) lines of 12 C 16 O 2 were observed on Venus with an infrared heterodyne spectrometer. The spectral resolution equals the Doppler half-width and the line profiles are fully resolved. The P (44) line was observed in June 1979 on the day side of the planet. The P (44) line core appears in absorption; the nonthermal core emission, which is present at low J values, is negligible at J = 44. Modeling of the line profile indicates that a discrete, optically thick, cloud deck occurs at 45 mbar pressure, in essential agreement with current understanding of the Venusian cloud structure. The 10.33- μ m R (8) line was observed in April 1980 at a variety of positions on the day side, and at a single position on the night side. The strong nonthermal core emission which appears on the day side for this line is not present on the night side, where the line core appears in absorption. This behavior is consistent with a solar radiative pump as an excitation mechanism for the nonthermal emission. Modeling of the R (8) night-side profile indicates that substantial high-altitude haze occurs above the cloud tops, in the region from 15 to 35 mbar pressure. Comparing the modeling for the R (8) line to the P (44) line we find that the variation in the mass of the high-altitude haze was greater than a factor of 2.