The analysis of the Voyager 2 Ultraviolet Spectrometer (UVS) solar occultation data obtained at Triton is consistent with a spherically symmetric, isothermal thermosphere above 400 km at T-=96 K. A detailed calculation of energy loss processes in a pure N2 atmosphere, heating and cooling rates, and resultant thermal structure associated with solar UV irradiance and magnetospheric electron precipitation indicates that solar heating, with calculated T-=70 K, is insufficient to account for the inferred T-=96 K. The magnetosphere must deposit twice as much power as the sun (&lgr;≤800 ¿) to heat the thermosphere to 96 K and generate the observed N2 tangential column densities above 450 km. The thermal escape of H and N atoms and the downward diffusion of N atoms to recombine below 130 km results in local ionospheric heating efficiency of 24%. An upper limit on the tropopause CO mixing ratio of 2¿10-4 is inferred in the absence of aerosol heating to balance its efficient cooling by LTE rotational line emission. ¿ American Geophysical Union 1992