WATER IN THE DEEP ATMOSPHERE OF VENUS FROM HIGH-RESOLUTION SPECTRA OF THE NIGHT SIDE

High-resolution, near-infrared (1.09 to 2.5 mu m) spectra of the night side of Venus have been obtained in 1990 and 1991 using the Fourier Transform Spectrometer at the 3.6-m Canada-France-Hawaii telescope. Absorptions due to H2O were detected in spectral windows near 2.3, 1.74, and 1.18 mu m. Our analysis of these absorptions constrains the abundance of water vapor in three different altitude ranges located between the clouds and the surface : 30-40 km, 15-25 km and 0-15 km. A constant water vapor mixing ratio of 30 +/- 15 ppm below the clouds can fit the observations. These values are consistent with recent near-infrared studies of the night side of Venus at lower spectral resolution. The atmosphere of Venus appears to be dryer than originally suggested by the in-situ measurements made by the Pioneer Venus and Venera mass-spectrometers and gas-chromatographs.