Photochemistry of phosphine and Jupiter's Great Red Spot.

Results from an experimental investigation of the ultraviolet photolysis of mixtures of phosphine (PH3) in hydrogen are presented. Solid phosphorus was produced by UV irradiation of mixtures of PH3 in hydrogen; the resulting product of this process was always yellow, not red, in color. The indices of refraction of the resulting elemental phosphorus were measured, and the scattering and absorbing properties of small spheres made of PH3 were computed. The reflectivities of these spheres were then compared with those observed for Jupiter's Great Red Spot. It was found that the phosphorus particles must be small (0.05 microns) and that their layer should have an optical depth of about one at a wavelength of 0.4 microns.