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

Abstract

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.