Volcanic control of the Io atmosphere and neutral and plasma torus

Rate equations for the column density of Io's atmosphere and the number density of neutral atoms and ions in the torus have been formulated in terms of surface sublimation and venting of volcanic gases, sputtering efficiency, thermal escape, and the plasma processes that take place in the torus which included electron impact ionization, charge exchange, and transport. In the limit of low volcanic activity, estimates of the densities can be obtained, and the baseline configuration that would exist in the absence of volcanic activity is found. Solution of the coupled steady state rate equations shows that the densities are sensitive, to a varying degree, to the level of Io volcanism. The steady state densities predicted by the model are consistent with a volcanic flux of no more than 10 to the 12th/sq cm per sec. This is significantly lower than the values obtained on the basis of resurfacing rates and appears to imply that surface lava flows play a major role in the resurfacing process.