Hybrid Fluid Model with Analytic/DSMC Thermal Escape in Pluto's Atmosphere

Details Hybrid Fluid Model with Analytic/DSMC Thermal Escape in Pluto's Atmosphere Hybrid Fluid Model with Analytic/DSMC Thermal Escape in Pluto's Atmosphere

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.4002e&link_type=abstract

American Astronomical Society, DPS meeting #42, #40.02; Bulletin of the American Astronomical Society, Vol. 42, p.999

Astronomy and Astrophysics

Astronomy

Scientific paper

Atmospheric escape from small bodies in the outer solar system is a highly active research problem, and is of particular interest with ongoing and future exploration missions. This requires modeling such atmospheres in both the low and high Knudsen number regimes (dense and tenuous, respectfully), with particular attention to the transition region between the two regimes. In many atmospheres of interest, non-thermal processes in the upper atmosphere drive escape. However, Pluto is an instance where heating in the lower atmosphere appears to drive the escape from the upper atmosphere.
There is no efficient method to model both regimes together due to vastly different length scales involved. Models like Slow Hydrodynamic Escape (SHE) use the in viscid fluid equation and apply them to the full atmosphere, and then fit the escape parameters to match an upper boundary condition at infinity or fit to measurement data. In place of an upper boundary condition, we require the escape parameters to agree with Jeans theory. From recent Direct-Simulated Monte-Carlo (DSMC) models, we believe that escape rates do not deviate significant from Jeans escape for atmospheres with moderate Jeans parameter.
When compared to SHE our solutions differ, yet with a sufficient heating rate the escape rates are comparable. Our model predicts a higher exobase altitude and temperature. We show that the affect of enhancement in actual escape rate (relative to Jeans escape) is lessened on the final escape rate in our model. We further use to model the upper atmosphere, and we are able to find a solution in both regimes that are consistent in escape rate and match profiles in a transition region.
AKNOWLEDGEMENTS
This report is funded in part by NASA.

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