THE DEEP ATMOSPHERE OF VENUS REVEALED BY HIGH-RESOLUTION NIGHTSIDE SPECTRA

THE night side of Venus is anomalously bright in two narrow spectral windows centred at 1.74 and 2.3 μm (ref. 1). The source of this emission has been identified recently as thermal radiation from atmospheric levels below the planet-wide decks of sulphuric acid cloud2-4. This emission provides a unique opportunity for remote-sensing investigations of the deep atmosphere of Venus. Here we report the first high-resolution (0.23 cm-1) spectroscopie observations of the night side of Venus obtained in these two windows. Absorption features from CO2, CO, H2O, HDO, HCl, HF and COS are detected, and there are a number of unidentified features. A preliminary analysis indicates that the observed radiation is thermal emission from atmospheric layers in the 8-bar pressure region for the 2.3-μm window and even deeper at 1.7 μm. The derived CO and H2O abundances agree with in situ measurements by Pioneer in the deep troposphere. Our analysis is also consistent with the high deuterium enrichment inferred from Pioneer data. We report the first measurements of HCl and HF below the clouds, along with the first firm detection of COS. These results will assist in the interpretation of the data from the Galileo encounter with Venus, and will provide new constraints on theoretical models of the atmospheric chemistry of Venus. © 1990 Nature Publishing Group.