Seminars

In July of 2015 the New Horizons space probe reached Pluto after nine years of travel, achieving the first close survey of the dwarf planet and its environs and vastly increasing our knowledge of that distant system. Motivated by the need to better understand and interpret the New Horizons (NH) observations, we apply here the direct simulation Monte Carlo (DSMC) rarefied gas dynamic technique in simulations of Pluto’s rarefied, non-equilibrium upper atmosphere. This novel three-dimensional model spans from several hundred km below the exobase – where continuum flow transitions to the rarefied regime – to fully free-molecular flow hundreds of thousands of km from Pluto’s center. We analyze the escape processes of N2 and CH4 from Pluto across a range of solar heating conditions, and evaluate the structure of the upper plutonian atmosphere including gas transfer to and deposition onto Charon.

Figure: (Left) Gas-transfer structures are noted in a binary atmospheric configuration, including a preferential deposition of material from Pluto’s escaping atmosphere onto Charon’s leading hemisphere. (Right, inset) As the moon gravitationally focuses incident flow, a high density structure forms in its wake.