  The upper atmospheres of Mars and Titan, as well as those on many other
planetary bodies, exhibit significant density variations vs. altitude that are
interpreted as gravity waves. Such data is then used to extract vertical
temperature profiles, even when such perturbations propagate through the
transition region from a collision dominated regime and into a planet's
exosphere. Since the temperature profile is critical for describing the upper
atmospheric heating and evolution, we use molecular kinetic simulations to
describe transient perturbations in a Mars-like upper atmosphere. We show that
the standard methods for extracting the temperature profile can fail
dramatically so that molecular kinetic simulations, calibrated to observed
density profiles, are needed in this region of a planet's atmosphere.
