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The photochemistry of methane in the atmosphere of Triton
Author(s) -
Strobel Darrell F.,
Simmers Michael E.,
Herbert Floyd,
Sandel Bill R.
Publication year - 1990
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl017i010p01729
Subject(s) - downwelling , atmosphere (unit) , atmospheric sciences , flux (metallurgy) , northern hemisphere , methane , photodissociation , troposphere , mixing ratio , zonal and meridional , southern hemisphere , trace gas , upwelling , physics , photochemistry , chemistry , geology , meteorology , oceanography , astronomy , organic chemistry
The photochemistry of methane in Triton's atmosphere is driven by approximately equal contributions of solar and local Interstellar medium (LISM) Lyα and in combination with weak vertical mixing, K ∼ 4 × 10 3 in the winter hemisphere and 8 × 10 3 cm 2 s −1 in the summer hemisphere, yields the observed CH 4 scale heights of ∼ 9 km below 70 km altitude (Broadfoot et al., 1989). The hemispheric difference in K is consistent with a seasonal meridional circulation with upwelling in the summer hemisphere and downwelling in the winter hemisphere. Methane photolysis produces H 2 molecules which are removed from the photolysis region by an upward flux ( ∼ 1.5 × 10 8 cm −2 s −1 , normalized to the surface) to the ionosphere where ion reactions convert H 2 to H. This results in a hydrogen escape flux of 3 × 10 8 cm −2 s −1 . The H column density is ∼ (5−10) × 10 14 cm −2 and resonantly scatters ∼ 26 R of solar Lya consistent with the day‐night asymmetry observed by the Voyager UVS. The inferred surface mixing ratios of CH 4 indicate subsaturated conditions. The CH 4 photolysis rate is sufficient to generate a smog of condensed C 2 H 2 , C 2 H 4 , C 2 H 5 , and C 4 H 2 particles in the lowest 30 km of Triton's atmosphere with an optical depth consistent with Voyager imaging results.