Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994icar..112..376t&link_type=abstract
Icarus (ISSN 0019-1035), vol. 112, no. 2, p. 376-381
Astronomy and Astrophysics
Astronomy
15
Atmospheric Energy Sources, Electron Energy, Haze, Hydrocarbons, Magnetospheric Electron Density, Titan, Albedo, Astronomical Models, Atmospheric Composition, Light Scattering, Photochemical Reactions, Radiative Transfer
Scientific paper
We present laboratory measurements of the radiation yields of complex organic solids produced from N2/CH4 gas mixtures containing 10 or 0.1% CH4. These tholins are thought to resemble organic aerosols produced in the atmospheres of Titan, Pluto, and Triton. The tholin yields are large compared to the total yield of gaseous products: nominally, 13 (C + N)/100 eV for Titan tholin and 2.1 (C + N)/100 eV for Triton tholin. High-energy magnetospheric electrons responsible for tholin production represents a class distinct from the plasma electrons considered in models of Titan's airglow. Electrons with E greater than 20 keV provide an energy flux approximately 1 x 10-2 erg/cm/sec, implying from our measured tholin yields a mass flux of 0.5 to 4.0 x 10-14 g/sq cm/sec of tholin. (The corresponding thickness of the tholin sedimentary column accumulated over 4 Gyr on Titan's surface is 4 to 30 m). This figure is in agreement with required mass fluxes computed from recent radiative transfer and sedimentation models. If, however, theses results, derived from experiments at approximately 2 mb, are applied to lower pressure levels toward peak auroral electron energy deposition and scaled with pressure as the gas-phase organic yields, the derived tholin mass flux is at least an order of magnitude less. We attribute this difference to the fact that tholin synthesis occurs well below the level of maximum electron energy depositon and to possible contributions to tholis from UV-derived C2-hydrocarbons. We conclude that Tita tholin, produced by magnetospheric electrons, is alone sufficient to supply at least a significant fraction of Titan's haze-a result consistent with the fact that the optical properties of Titan tholin, among all proposed material, are best at reproducing Titan's geometric albedo spectrum from near UV to mid-IR in light-scattering models.
McDonald Gene D.
Reid Thompson W.
Sagan Carl
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