Molecular Absorption and the Possible Structure of the Cloud Layers of Jupiter and Saturn

Open Access
Publisher Website
Google Scholar
Abstract
This paper deals with spectrographic and spectrophotoelectric observations of the absorption bands of CH4 at 6190 and 7250 Å and NH3 at 6450 Å, in the spectra of Jupiter and Saturn carried out in recent years. In the dark matter of the Jovian cloud layer the methane absorption is 15–20% greater than that in the light matter. The presence of bright polar caps on Jupiter in the infrared CH4 bands at 8860 and 9870 Å is confirmed by spectrograms obtained with the electronic image tube. The methane and ammonia absorption diminishes towards the limb on Jupiter. There is no correlation between the absorption of CH4 and the color of the cloud belts. In the Red Spot, as shown by the measurements of many spectrograms in 1964 and 1969, the intensities of the methane band at 6190 Å are the ammonia band at 6450 Å are the same as in the neighboring regions of the South Tropical Zone. On Saturn the CH4 absorption at 6190 and 7250 Å in the bright equatorial zone in 1966 and 1998 was 20–25% less than in the temperate dark belt. The absorption increases with latitude but is diminished near the poles and decreases along the equator toward the east and west limbs. Ultraviolet pictures of Saturn obtained by Marin at the Pic du Midi Observatory show brightening toward the limb. This result indicates that the decrease of the CH4 absorption from the center to the equatorial limb of Saturn cannot he explained by an increase of the altitude of the cloud boundary near the limb. The distribution of molecular absorption on the disks of Jupiter and Saturn may be satisfactorily explained by the effects of multiple scattering in the cloud layers of these planets if the density of the clouds is not very high (the volume scattering coefficient σ ∼ 10−7 cm−1 for the case of isotropic scattering). The differences in the absorption of the bright and dark matter may explained by changes of cloud density by a factor of 1.5–2. The abundance of CH4 and NH3 in the outer (overcloud) atmosphere must be diminished by a factor of 4–6 as compared with estimates based on a model of simple reflection from the cloud layer. The temperature of the Red Spot on Jupiter cannot be different by wore than 1–2K from that in the South Tropical Zone. Theoretical calculations of the planetary line profiles show that the effects of multiple scattering in the diluted cloud layer may he responsible for the observed decrease of the infrared methane absorption in the dark equatorial belts of Jupiter.

This publication has 0 references indexed in Scilit: