870 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
Predictions of the atmospheric composition of GJ 1132b
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is
amongst the most highly characterizable small exoplanets currently known. In
this paper we study the interaction of a magma ocean with a water-rich
atmosphere on GJ 1132b and determine that it must have begun with more than 5
wt% initial water in order to still retain a water-based atmosphere. We also
determine the amount of O2 that can build up in the atmosphere as a result of
hydrogen dissociation and loss. We find that the magma ocean absorbs at most
~10% of the O2 produced, whereas more than 90% is lost to space through
hydrodynamic drag. The most common outcome for GJ 1132 b from our simulations
is a tenuous atmosphere dominated by O2, although for very large initial water
abundances atmospheres with several thousands of bars of O2 are possible. A
substantial steam envelope would indicate either the existence of an earlier H2
envelope or low XUV flux over the system's lifetime. A steam atmosphere would
also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2 or N2-rich atmospheres on GJ
1132 b.Comment: 14 pages, 11 figures, accepted at Ap
Atmospheric Chemistry of Venus-like Exoplanets
We use thermodynamic calculations to model atmospheric chemistry on
terrestrial exoplanets that are hot enough for chemical equilibira between the
atmosphere and lithosphere, as on Venus. The results of our calculations place
constraints on abundances of spectroscopically observable gases, the surface
temperature and pressure, and the mineralogy of the surface. These results will
be useful in planning future observations of the atmospheres of
terrestrial-sized exoplanets by current and proposed space observatories such
as the Hubble Space Telescope (HST), Spitzer, James Webb Space Telescope
(JWST), Terrestrial Planet Finder, and Darwin.Comment: 35 pages, 4 figures, 3 tables; 1 appendix; submitted to ApJ; version
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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