  A self-consistent, aeronomic model of the upper atmosphere of a "hot Jupiter"
including reactions involving suprathermal photoelectrons is presented. This
model is used to compute the height profiles of the gas density, velocity, and
temperature in the atmosphere of the exoplanet HD 209458b. It is shown that
including suprathermal electrons when computing the heating and cooling
functions reduces the mass loss rate of the atmosphere by a factor of five.
