Methane, Ammonia, and Temperature Measurements of the Jovian Planets and Titan from CCD–Spectrophotometry

Abstract

Full-disk albedo spectra of the jovian planets and Titan were derived from observations at the European Southern Observatory in July 1995. The spectra extend from 300 to 1050 nm wavelength. The spectral resolution is 0.4 nm between 520 and 995 nm, and 1 nm elsewhere. The accuracy of the albedo calibration is 4%. UBV magnitudes were also determined. Raman scattering was quantified for each planet. Methane and ammonia bands are shown at 0.4 nm spectral resolution, including a new band at 930 nm wavelength which is probably due to ammonia. Maps of the variation of these absorptions across the disks of Jupiter and Saturn are displayed. Saturn's spectrum is undisturbed by light from its rings due to the edge-on geometry during the observations. The albedo of Uranus near 1 μm wavelength has dropped almost 10% between 1993 and 1995, while there has been no change in the ultraviolet. The signature of light from Titan's surface yielded a path length of 4 km-am of methane in Titan's atmosphere. The temperature dependence of the width of the 890-nm methane band was used to measure temperature variations at three altitude levels, resulting in the first temperature maps of Jupiter and Saturn based on reflected sunlight. Jupiter displays a banded temperature structure with some discrete features of a few Kelvin amplitude. Saturn's north–south temperature asymmetry has reversed since the Voyager observations.