Auroral ultraviolet darkening on the outer planets
The Voyager 2 Photopolarimeter Subsystem (PPS) has made photometric observations of Jupiter at 2400 A and photometric and polarimetric observations of Saturn and Uranus at 2650 A. At these wavelengths the instrument is observing each planet's stratosphere and upper troposphere. The most striking features are that both poles of Jupiter and the observed northern pole of Saturn are very dark, while Uranus has a uniformly bright appearance. All three planets show evidence for a stratospheric haze. Simple vertically homogeneous multiple scattering models are used to characterize these stratospheric hazes. Aurores occur at high latitudes on Jupiter and Saturn and at low latitudes on Uranus. The asymmetric polar darkening on Jupiter seen by PPS is roughly matched by the asymmetry in the auroral zones. Historical data suggest that the haze asymmetry is persistent. The dark north polar cap seen by PPS at Saturn is small and close to the pole, which corresponds to the small auroral zone close to the pole. A model is examined which attributes the darkening to auroral bombardment initiating methane chemistry that makes dark hydrocarbon particles. Possible chemical pathways are discussed, and mass balance calculations are presented for Jupiter, Saturn, and Uranus. The model is quantitatively plausible for Jupiter and Saturn. The lack of localized darkening on Uranus can be explained in this model by noting that weak vertical mixing and methane condensation near the 1-bar level lead to negligible methane abundances at auroral altitudes. The auroras must reach the methane for dark material to form. The thin haze that is seen on Uranus is ascribed to photochemical processes. Voyager 2 will reach Neptune this year. Ground-based observers have reported vigorous vertical mixing and large amounts of stratospheric methane there.
- Research Organization:
- Colorado Univ., Boulder, CO (USA). Cooperative Inst. for Research in Environmental Sciences
- OSTI ID:
- 6688206
- Resource Relation:
- Other Information: Ph.D. Thesis
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
JUPITER PLANET
PLANETARY ATMOSPHERES
NEPTUNE PLANET
SATURN PLANET
URANUS PLANET
ABUNDANCE
AURORAE
CHEMICAL COMPOSITION
EXPERIMENTAL DATA
HYDROCARBONS
MASS DISTRIBUTION
METHANE
PHOTOCHEMICAL REACTIONS
PHOTOMETRY
POLARIMETERS
SCATTERING
ALKANES
ATMOSPHERES
CHEMICAL REACTIONS
DATA
DISTRIBUTION
INFORMATION
NUMERICAL DATA
ORGANIC COMPOUNDS
PLANETS
SPATIAL DISTRIBUTION
640107* - Astrophysics & Cosmology- Planetary Phenomena