HR: 0830h
AN: P21B-04    [Abstracts]
TI: Theory of "Optically-Thick" ENA Emission from Titan's Exosphere
AU: * Roelof, E C
EM: edmond.roelof@jhuapl.edu
AF: Johns Hopkins University/Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723-6099 United States
AB: The brightest energetic neutral atom (ENA) emission from Titan's inner exosphere is produced by energetic singly-charged ions undergoing multiple atomic collisions with the cold exospheric atoms at altitudes above 1500 km. Any proper transport theory of this "optically-thick" ENA emission must include all categories of atomic collisions (charge-exchange, stripping, ionization, and excitation) for both energetic ions and ENAs. The energies of the hydrogen and oxygen ENAs imaged by the Cassini/MIMI/INCA camera are above 10 keV/nuc, so the gyroradii of the ions producing the ENAs imaged by INCA are comparable to, or exceed the radius of Titan (2575 km) in a 5nT magnetic field. In this regime, the cross-sections for all collisions are very strongly peaked in the forward direction. These two afore-mentioned facts allow an analytic solution to the "optically-thick" coupled transport equations for ions and ENAs in terms of simple (exponential) functions. The resulting formulas for the ENA intensity as a function of the energetic ion intensity (spectrum and spatial distribution) are presented along with some simulated images. Relevant INCA observations are presented by Dandouras et al. and Brandt et al. elsewhere in this Special Session.
DE: 2459 Planetary ionospheres (5435, 5729, 6026, 6027, 6028)
DE: 5405 Atmospheres--composition and chemistry
DE: 6207 Comparative planetology
DE: 6275 Saturn
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly