K. H. Baines

Interpretation of the 6818.9-Å methane feature observed on Jupiter, Saturn, and Uranus☆

Abstract High-resolution (0.1-A) spectra of the 6818.9-A methane feature obtained for Jupiter, Saturn, and Uranus by K. H. Baines, W. V. Schempp, and W. H. Smith ((1983) . Icarus 56 , 534–542) are modeled using a doubling and adding code after J. H. Hansen ((1969) . Astrophys. J. 155 , 565–573). The features rotational quantum number is estimated using the relatively homogeneous atmosphere of Saturn, with only J = 0 and J = 1 fitting the observational constraints. The aerosol content within Saturns northern temperate region is shown to be substantially less than at the equator, indicating a haze only half as optically thick. Models of Jupiters atmosphere are consistent with the rotational quantum-number assignment. Synthetic line profiles of the 6818.9-A feature observed on Uranus reveal that a substantial haze exists at or above the methane condensation region with an optical depth eight times greater than previously reported. Seasonal effects are indicated. The methane column abundance is 5 ± 1 km-am. The mixing ratio of methane to hydrogen within the deep unsaturated region of the planet is 0.045 ± 0.025, based on an H 2 column abundance of 240 ± 60 km-am ( W. H. Smith, W. Macy, and C. B. Pilcher (1980) . Icarus 43 , 153–160), thus indicating that the methane comprises between one-sixth and one-half of the planets mass. However, proper reevaluation of H 2 quadrupole features accounting for the haze reported here may significantly reduce the relative methane abundance.

Spatially resolved absolute spectrophotometry of Saturn - 3390 to 8080 A

Abstract Absolute spectrophotometry of four regions on the visible disk of Saturn (north and south polar regions, equatorial band, south “temperate” region) from 3390 to 8080 A is reported. Spectral resolution is 10 A in the interval 3390–6055 A, and 20 A; aperture size is 1.92 arcsec. The explicit purpose of our observations was to provide ground-based photometric calibration for the Pioneer Saturn Imaging Photopolarimeter (IPP). We also compare our data with earlier spectrophotometric measurements of Saturn ( R.L. Younkin and G. Munch, 1963 ,Mem. Soc. Roy. Sci. Liege 7, 123–136; W.M. Irvine and A.P. Lane, 1971 ,Icarus 16, 10–26; T.B. McCord, T.V. Johnson, and J.H. Elias, 1971 ,Astrophys. J. 165, 413–424) and with the M. Podolak and R.EE. Danielson (1977) Icarus 30, 479–492) parameterization of “Axel Dust.” The latter reproduces the broad features but not the details of the observed spectral reflectivity (I/F). We find that large depths of clear molecular hydrogen (>14 km-am in the temperate regions) are needed to match the observed upturn in reflectivity shortward of 3800 A.

Limits on the diurnal variation of H2 quadrupole features in Neptune

Spectral profiles of the H2 S4(0) and S4(1) lines are presented for Neptune on three consecutive nights; no variation is detected in the equivalent widths of the H2 4-0 features to within an observational uncertainty of about 20 percent. Comparisons with previous H2 quadrupole observations indicate that no secular trends have been detected over about 15 yr. The equivalent-width error limits are interpreted in terms of the maximum variability of Neptunian tropospheric aerosols. Specifically, the error bars for the globally averaged equivalent widths of the two H2 quadrupole absorption features constrain the bottom of the visible atmosphere, as defined by a bright optically infinite isotropically scattering cloud, to be 2.9 + or - 0.6 bars, while the methane haze opacity is constrained to be 0.30 + or - 0.25. 43 refs.