  The role of charge exchange in shaping exoplanet photoevaporation remains a
topic of contention. Exchange of electrons between stellar wind protons from
the exoplanet's host star and neutral hydrogen from the planet's wind has been
proposed as a mechanism to create "energetic neutral atoms" (ENAs), which could
explain the high absorption line velocities observed in systems where mass loss
is occurring. In this paper we present results from 3D hydrodynamic simulations
of the mass loss of a planet similar to HD 209458b. We self-consistently launch
a planetary wind by calculating the ionization and heating resulting from
incident high-energy radiation, inject a stellar wind into the simulation, and
allow electron exchange between the stellar and planetary winds. We predict the
potential production of ENAs by the wind-wind interaction analytically, then
present the results of our simulations, which confirm the analytic limits.
Within the limits of our hydrodynamic simulation, we find that charge exchange
with the stellar wind properties examined here is unable to explain the
absorption observed at high Doppler velocities.
