Chemical processes in Triton's atmosphere and surface |
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| Institution: | 1. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, PR China;2. Nuclear Graphite Research Group, Department of MACE, The University of Manchester, M13 9LP, UK;3. Dalton Cumbrian Facility, The University of Manchester, Westlakes Science & Technology Park, Moor Row, Cumbria CA24 3HA, UK;1. NASA Goddard Space Flight Center/USRA, Greenbelt, MD 20771, USA;2. ESTEC, European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands;3. Smithsonian Institution, National Air and Space Museum, Center for Earth and Planetary Studies (CEPS), Washington, DC 20560, USA;4. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA;5. Department of Geophysics, Faculty of Mathematics and Physics, Charles University, 180 00 Prague, Czech Republic;6. Institute of Geophysics of the Czech Academy of Science, 141 31 Prague, Czech Republic;7. Deutsches Zentrum für Luft- und Raumfahrt (DLR), 12489 Berlin, Germany;8. U. S. Geological Survey, Flagstaff, AZ 86001, USA;9. Jet Propulsion Laboratory, Caltech, Pasadena, CA 91125, USA;10. Institut für Planetologie, Westfälische Wilhelms-Universität, 48149 Münster, Germany;11. NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;12. Max-Planck-Institut für Sonnensystemforschung (MPS), 37007 Göttingen, Germany;13. Institute of Geological Sciences, Freie Universität Berlin, 12249 Berlin, Germany;14. Lunar and Planetary Institute, Houston, TX 77058, USA;15. Planetary Science Institute, Tucson, AZ 85719, USA;p. School of Earth & Space Exploration, Arizona State University, Tempe, AZ 85004, USA;q. Earth, Planetary and Space Sciences, UCLA, Los Angeles, CA 90095, USA |
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| Abstract: | Liquid solutions of N2 containing up to one-third CH4 can exist on Triton's surface in regions T > 62.5°K. More generally, subsurface oceans of N2 solution are expected to be stable beneath overlying, thermally insulating, less dense layers of the abundant light hydrocarbon products of radiochemical synthesis: C2H6, C3H8, and C4H10. Cosmic rays are the main source of energy, capable of producing synthesis of organic compounds from N2CH4 solutions on the surface. For baseline Triton models with R = 2500 km, ϱ = 2.1 g cm−3, and Ts = 65 or 55°K, respectively, 4 × 10−3 or 7 × 10−3 erg cm−2 sec−1 (49 or 87% of the total incident flux) is deposited within a few meters below the surface. Using yields from laboratory experiments, we estimate the quantities of products produced: over 4.5 billion years, the cosmic ray flux alone produces 2 to 4 m of organic product, about half of which is C2H6. For ocean depths <250 m, C2H6 will reach its saturation limit and form a surface “slick.” For ocean depths <10 km, all of the other products also oversaturate and exsolve, adding to the surface slick and/or to a denser bottom sediment. Products produced from solid N2CH4 mixtures will accumulate as evaporite deposits because of the rapid volatile transport (of N2 and CH4) over Triton's surface. The complex, reddish organic solid found in laboratory simulations is probably the source of Triton's reddish color. Estimated yields over 4.5 billion years (for 7 × 10−3 erg cm−2 sec−1) are 190 (C2H6), 58 (NH3), 17 (HCN), 3.5 (HN3), 2.5 (C4H10), 0.35 (CH3CN), and 0.14 (C2H5N3) g cm−2. More basic laboratory work on the low-temperature, low-pressure solvent properties and phase equilibria of N2-hydrocarbon systems is clearly needed. |
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