A model of Triton's atmosphere and ionosphere

On the basis of Voyager 2 observations, a simple model of Triton's thermosphere and ionosphere is built. Heating and ionization by solar EUV and precipitating electrons are computed. Our main conclusions are: (i) solar EUV flux at Triton is large enough to account for the observed exospheric temperature (95 K), but not for the observed electron densities (ii) Although N₂⁺ is the principal product of ionization, it is rapidly quenched in collisions with CH₄ or H₂ and N⁺ is the major ion (iii) the ionosphere is in chemical equilibrium below 700 km and in diffusive equilibrium above (iv) Ionization by a maxwellian distribution of precipitating electrons with average energy 900 eV and total input 0.1 erg cm^-3 s^-1 can reasonably well account for the observed ionosphere.