Gas Transfer in the Pluto-Charon System: A Charon Atmosphere

Orenthal J Tucker, NASA Goddard Space Flight Center, Greenbelt, United States, Robert E Johnson, University of Virginia, Materials Science and Engineering, Charlottesville, United States, Leslie Ann Young, Southwest Research Institute Boulder, Boulder, CO, United States, Xianzhe Jia, University of Michigan, Department of Climate and Space Sciences and Engineering, Ann Arbor, United States and Valeriy Tenishev, University of Michigan, Climate and Space Sciences and Engineering, Ann Arbor, United States
Abstract:
Recent hybrid fluid/molecular kinetic models demonstrated that Pluto’s upper atmosphere is warmer and more extended than previously thought (Erwin et al., 2013; Tucker et al. 2012). This extended atmosphere is a source of molecules to Charon’s surface. For approximate solar medium conditions at ~33AU about ~0.2% of the flux from Pluto’s exobase impinges on Charon at a rate of ~5.7×1025 N2/s. This is a source of condensed N2 for Charon’s night side, and molecules re-emitted from warmer (>20 K) surface regions form a tenuous atmosphere. For the approximate range of surface temperatures, the residence time of N2 on the surface can range from a fraction of a second to 10’s of years with the near surface line of sight column densities varying from ~3×1018 N2/m2 up to >6×1019N2/m2. Additional mechanisms that can eject N2molecules from the surface include cometary impacts (Stern et al. 2014) and electronic sputtering (Johnson et al., 2013). A Charon atmosphere could be detectable during the solar occultation that will occur during the New Horizon encounter providing a measure of the transfer of gas between bodies in this binary system.

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Stern, S.A., R. Gladstone, A. Zangari, D. Goldstein,T.Fleming 2014. Transient Atmospheres on Charon and Other Water-Ice Covered KBOs, Resulting from Comet Impacts, Icarus. DOI: 10.1016/j.icarus.2014.03.008

Johnson, R.E., R. Carlson, T.A. Cassidy, M. Fama, "Sputtering of ices", Chapter in The Science of Solar System Ices. ed. M. Gutopati, J. Castillo-Rogez, Astrophysics and Space Science Library, 356, pp551-581 (2013).

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