Galileo Photopolarimeter-Radiometer Observations of Jupiter and the Galilean Satellites

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Science  18 Oct 1996:
Vol. 274, Issue 5286, pp. 389-391
DOI: 10.1126/science.274.5286.389


Photopolarimeter-Radiometer (PPR) maps of daytime temperatures on Ganymede at a resolution of 220 kilometers show the expected anticorrelation with albedo, but morning temperatures were about 10 kelvin warmer than expected. Europa had a subsolar temperature of 128 kelvin and a lower effective thermal inertia than either Ganymede or Callisto, and Io's night side was cooler than predicted by recent models, perhaps requiring revision of heat-flow estimates. The lowest 250-millibar temperatures in the Great Red Spot (GRS) generally corresponded to the visually darkest regions. Temperatures remained cold north of the GRS, but they rose by as much as 6 kelvin to the south over the 2800-kilometer PPR resolution. A visually bright region northwest of the GRS was also relatively cold. It is likely that NH3 clouds affected the determination of the 500-millibar temperature field, which appears qualitatively different.