Premium
Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape
Author(s) -
Bell Jared M.,
Hunter Waite J.,
Westlake Joseph H.,
Bougher Stephen W.,
Ridley Aaron J.,
Perryman Rebecca,
Mandt Kathleen
Publication year - 2014
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2014ja019781
Subject(s) - titan (rocket family) , thermosphere , methane , atmospheric escape , atmosphere (unit) , atmospheric sciences , atmosphere of titan , ionosphere , physics , atmospheric models , atmospheric chemistry , atmospheric model , environmental science , thermal , astrobiology , meteorology , chemistry , geophysics , ozone , organic chemistry , mars exploration program
Abstract In this study, we develop a best fit description of Titan's upper atmosphere between 500 km and 1500 km, using a one‐dimensional (1‐D) version of the three‐dimensional (3‐D) Titan Global Ionosphere‐Thermosphere Model. For this modeling, we use constraints from several lower atmospheric Cassini‐Huygens investigations and validate our simulation results against in situ Cassini Ion‐Neutral Mass Spectrometer (INMS) measurements of N 2 , CH 4 , H 2 , 40 Ar, HCN, and the major stable isotopic ratios of 14 N/ 15 N in N 2 . We focus our investigation on aspects of Titan's upper atmosphere that determine the amount of atmospheric escape required to match the INMS measurements: the amount of turbulence, the inclusion of chemistry, and the effects of including a self‐consistent thermal balance. We systematically examine both hydrodynamic escape scenarios for methane and scenarios with significantly reduced atmospheric escape. Our results show that the optimum configuration of Titan's upper atmosphere is one with a methane homopause near 1000 km and atmospheric escape rates of 1.41–1.47 ×10 11 CH 4 m −2 s −1 and 1.08 ×10 14 H 2 m −2 s −1 (scaled relative to the surface). We also demonstrate that simulations consistent with hydrodynamic escape of methane systematically produce inferior fits to the multiple validation points presented here.