Photometry of Venus below 2200 Å from the orbiting astronomical observatory-2

Spectrophotometry of Venus from 2170 to about 1950 Å has been obtained by OAO-2 at 10 Å resolution. The new data confirm and extend previous indications that the geometric albedo decreases continuously below 2500 Å. Secular changes in either the amount or distribution, or both, of absorbing constituents in the upper atmosphere are strongly suggested. A narrow absorption feature is found near 2145 Å, confirming an earlier report by Anderson et al. [J. Atmos. Sci.26 (1969), 874–888]. Absorption by trace amounts of nitrogen-bearing molecules, including N₂O, HNO₃ in aqeous solution, and possibly also NO, together with Rayleigh scattering from CO₂, can account for the variation in albedo below 3200 Å, but other explanations are not excluded. For example, H₂S may contribute to or be responsible for the decrease in albedo below 2500 Å.