Zonally averaged thermal balance and stability models for nitrogen polar caps on Triton

We have analyzed Voyager four color imaging data of Triton to calculate the bolometric hemispheric as a function of latitude and longitude. Zonal averages of these data have been incorporated into a thermal balance model involving insolation, reradiatation and latent heat of sublimation of N₂ ice for the surface. The current average bolometric albedo of Triton's polar is 0.8, implying an effective temperature of 34.2K and a surface pressure of N₂ of 1.6 μb for unit emissivity. This pressure is an order of magnitude lower than the surface pressure of 18 μb inferred from Voyager data [Broadfoot et al., 1989; Conrath et al., 1989], a discrepancy that can be reconciled if the emissivity of the N₂ on Triton's surface is 0.66. The model predicts that Triton's surface north of 15° N latitude is experiencing deposition of N₂ frosts, as are the bright portions of the south polar cap near the equator. This result explains why the south cap covers the entire southern hemisphere of Triton. Initial results from a seasonal model are also described briefly, although they do not agree with the Voyager observations.