Models of Pluto‧s upper atmosphere

Abstract

Best guesses as to the thermal structure and composition of Pluto‧s atmosphere have led to speculations of substantial loss rates (∼1028 s−1) of methane from the planet over cosmogonic time scales. Results from recent stellar occultation measurements, and using a Parker‐type hydrodynamic calculation, show that the loss rates may actually be lower by as much as a factor ∼5, depending upon the efficiency of heating of the atmosphere via the absorption of solar EUV and upon the true atmospheric composition, if the thermal structure of the upper atmosphere is properly taken into account. The loss rate may even be less (by another factor ∼10) if there is minimal heating of the upper atmosphere.