Spectrophotometry of the Jovian Planets and Titan at 300- to 1000-nm Wavelength: The Methane Spectrum

Full-disk albedo spectra of the jovian planets and Titan were derived from observations at the European Southern Observatory in July 1993. The spectra extend from 300- to 1000-nm wavelength at 1-nm resolution. The signal-to-noise ratio is approximately 1000 in the visible. The accuracy is 2% for relative and 4% for absolute ulbedos. Colors and magnitudes were also determined. Some 40-60 Raman scattering features are visible in the spectrum of each jovian planet. A Raman scattering model with five parameters adjusted for each planet can explain these features. A methane absorption spectrum is given which fits methane features in the spectra of the jovian planets and Titan. It differs from room-temperature laboratory spectra but it is consistent with some limited laboratory data at cold temperatures. Three new, weak methane bands were detected in the spectra of Uranus and Neptune. A strong absorption hand in Jupiter's spectrum is possibly due to water, confirming a strong depletion of oxygen in the probed part of Jupiter's atmosphere.