Simulating Pluto’s atmosphere with hybrid fluid/kinetic models
Justin Erwin
Recent and expected spacecraft exploration of the planets and moons of our solar system
have greatly increased interest in atmospheric escape. My motivation has been to produce
an accurate model of Pluto’s atmosphere, which includes atmospheric loss by escape. The
results will be both predictive for and tested against data obtained during the New
Horizon encounter, which will occur in late 2015.
To accurately capture the nature of the escape and structure of Pluto’s thermosphere and
exosphere, I have developed a model of Pluto’s upper atmosphere by connecting a fluid
model to a molecular kinetic model. Using this hybrid model I have shown that the
atmosphere is much more extended than previously predicted and the escape is not
supersonic, as in comet or stellar atmospheres. Rather, it is closer to the evaporative Jeans
model of escape. Furthermore, I have developed a self-consistent model of Pluto’s full
atmosphere, including both the stratospheric radiative heating and cooling that prevail in
the lower atmosphere, as well as the UV heating and the cooling by atmospheric escape.