Abstract
It is likely that proto-Titan accumulated hydrogen molecules from the Saturnian subnebnula and kept a proto-atmosphere with surface pressure of several hundred bars. Once the subnebula began to dissipate, this proto-atmosphere should have escaped as the pressure of the astmosphere decreased at the upper boundary. We have developed a numerical hydrodynamic model similar to that for solar wind, and solved the escape of the proto-atmosphere. If the density of the subnebula becomes less than that of the atmosphere with factor of 10-1, the intense escape occurs and could lose the almost all of the proto-atmosphere for several hundred years. We also argue the effects of the such vigorous escape on the composition of the unescaped atmospheric components.
