PLUTO EXTENDED ATMOSPHERE - AN ESCAPE MODEL AND INITIAL OBSERVATIONS

We have calculated the rates of production and hydrodynamic outflow of atomic hydrogen resulting from the photodissociation of methane in the upper atmosphere of Pluto. Under the present near-perihelion conditions this yields an extended cloud of H around Pluto which is likely to be the most easily observable signature of Pluto's extended atmosphere, and thereby provide information on the extent, escape rate, and composition of Pluto's upper atmosphere. We have also performed initial observations with the IUE attempting to detect the H Ly α emission from the extended H cloud, which we use to derive upper limits to the cloud properties as a function of the cloud extent. © 1992.