Ultraviolet observations of Mars and Saturn by the TDIA and OAO-2 satellites

Ultraviolet photometric and spectrophotometric observations of Mars and Saturn obtained by two Earth-orbiting satellites are combined in this report. High-resolution data from the S59 experiment aboard TD1A reveal no definite absorption features in the spectra of either planet. The absence of a prominent absorption in the Mars data near 2150 Å can be reconciled with the preliminary Viking measurement of NO only if that gas is preferentially concentrated at high Martian altitudes. Broadband photometry from OAO-2 shows that atmospheric dust on Mars during the great dust storm of 1971–1972 reduced the ultraviolet geometric albedo by a factor of ?3 at the height of the storm. This atmospheric energy deposition is probably an important mechanism in the storm dynamics. Diurnal variation in the ultraviolet brightness of Mars appears to be marginally detectable during the dust storm. A real brightness variation during a clear season is observed. The combined Saturn data from the two satellites strongly suggest that NH₃ does not influence the ultraviolet spectrum of Saturn, but that some other absorber does. A candidate for such an absorber, H₂S, is investigated. OAO-2 broadband photometry of Jupiter and of Saturn demonstrate that these planets have very similar albedos from 2100 to 2500 Å. This implies a common ultraviolet absorber on both planets, other than NH₃.