Gas Transfer in the Pluto-Charon System: A Charon Atmosphere
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.
Tucker, O.J., Erwin, J.T., Deighan, J.I., Volkov, A.N., Johnson, R.E., 2012. Thermally driven escape from Pluto’s atmosphere: A combined fluid/kinetic model. Icarus 217, pp 408-415.;
Erwin, J.T., Tucker, O.J., Johnson, R.E., 2013. Hybrid fluid/kinetic modeling of Pluto’s escapingatmosphere. Icarus 226, 375-384.
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).