4,177 research outputs found
Silicon Tetrafluoride on Io
Silicon tetrafluoride (SiF4) is observed in terrestrial volcanic gases and is
predicted to be the major F - bearing species in low temperature volcanic gases
on Io (Schaefer and Fegley, 2005b). SiF4 gas is also a potential indicator of
silica-rich crust on Io. We used F/S ratios in terrestrial and extraterrestrial
basalts, and gas/lava enrichment factors for F and S measured at terrestrial
volcanoes to calculate equilibrium SiF4/SO2 ratios in volcanic gases on Io. We
conclude that SiF4 can be produced at levels comparable to the observed
NaCl/SO2 gas ratio. We also considered potential loss processes for SiF4 in
volcanic plumes and in Io's atmosphere including ion-molecule reactions,
electron chemistry, photochemistry, reactions with the major atmospheric
constituents, and condensation. Photochemical destruction (tchem ~ 266 days)
and/or condensation as Na2SiF6 (s) appear to be the major sinks for SiF4. We
recommend searching for SiF4 with infrared spectroscopy using its 9.7 micron
band as done on Earth.Comment: 16 pages, 2 figures, 1 table; Icarus, in pres
Operational limitations in flying noise- abatement approaches
Operational limitations in flying noise abatement approache
NASA research on noise-abatement approach profiles for multiengine jet transport aircraft
NASA research on noise-abatement steepened approaches for multiengine jet transport
Alkali and Halogen Chemistry in Volcanic Gases on Io
We use chemical equilibrium calculations to model the speciation of alkalis
and halogens in volcanic gases emitted on Io. The calculations cover wide
temperature (500-2000 K) and pressure (10^-6 to 10^+1 bars) ranges, which
overlap the nominal conditions at Pele (T = 1760 K, P = 0.01 bars). About 230
compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are
considered. We predict the major alkali and halogen species in a Pele-like
volcanic gas and the major alklai and halogen condensates. We also model
disequilibrium chemistry of the alkalis and halogens in the volcanic plume.
Based on this work and our prior modeling for Na, K, and Cl in a volcanic
plume, we predict the major loss processes for the alkali halide gases are
photolysis and/or condensation onto grains. On the basis of elemental
abundances and photochemical lifetimes, we recommend searching for gaseous KCl,
NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during
eruptions. Based on abundance considerations and observations of brown dwarfs,
we also recommend a search of Io's extended atmosphere and the Io plasma torus
for neutral and ionized Li, Cs, Rb, and F.Comment: 32 pages, 4 tables, 5 figures; accepted for publication by Icaru
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