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  • 1
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    Supersonic meteorology of Io - Sublimation-driven flow of SO2 (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The horizontal flow of SO2 gas from the day side to the night side of IO is calculated on the basis of a hydrodynamic model. The flow speed is found to be supersonic for all realistic values of the parameters. The surface pressure follows the frost vapor pressure within a factor of 2 in spite of day-night pressure ratios of 10,000 or more. Atmospheric temperature is generally below the surface temperature due to decompression in the expanding flow. The greatest sensitivity of the solution is connected with the frost temperature at the subsolar point. The quantities that involve the mass of the atmosphere (density, pressure, mass transport, and condensation rate) all vary as the vapor pressure of the frost, which is a sensitive function of frost temperature.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 64; 375-390
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  • 2
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    Diurnal variations of mesospheric ozone obtained by ground-based microwave radiometry (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: From December 1986 until April 1987 ground-based microwave observations of the diurnal variation of mesospheric ozone were made over Bern, Switzerland. These data were of sufficient quality to define the characteristics diurnal behavior of the ozone mixing ratio during winter and equinoctial conditions. The observed diurnal variation of ozone peaks at about 74 km, where its amplitude is about a factor of 6. At 65 km the observed diurnal variation is a factor of 3, whereas at 55 km it is only a factor of 1.4. One-dimensional model calculations accurately reproduce the relative diurnal variation of ozone at equinox, suggesting that the model value of the ozone photolysis rate coefficient is accurate to better that 10 percent. For winter conditions, however, the model underpredicts the observed relative diurnal variation by a factor of 2; a major part of this discrepancy is due to an observed postmidnight increase in ozone. Various suggested changes in model parameters to better produce the ozone abundance vertical profile result in only small differences in the relative diurnal variation, indicating that these observations do not provide a sensitive test of the mesospheric chemistry controlling the abundance of odd oxygen.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 12819-12
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  • 3
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    A model study of the response of mesospheric ozone to short-term solar ultraviolet flux variations (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An investigation is conducted in order to determine the relative importance of several modeled processes in controlling the magnitude and phase of the mesospheric ozone response. A detailed one-dimensional modeling study of the mesospheric ozone response to solar UV flux variations is conducted to remove some of the deficiencies in previous studies. This study is also used to examine specifically the importance of solar zenith angle, self-consistent calculation of water vapor abundance, and temperature feedback with a nonlocal thermodynamic equilibrium radiation model. The photochemical model is described, and the assumptions made for the purpose of comparing model results with the observed ozone response obtained from a statistical analysis of Solar Mesosphere Explorer data (Keating et al., 1987) are discussed. The numerical results for the theoretical ozone response are presented. The results of selected time-dependent calculations are considered to illustrate the degree to which a relatively simple model of the mesosphere is able to capture the major characteristics of the observed response.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 22523-22
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  • 4
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    Non-Equilibrium Thermodynamic Chemistry and the Composition of the Atmosphere of Mars (2003)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: A high priority objective of the Mars Exploration Program is to Determine if life exists today (MEPAG Goal I, Objective A). The measurement of gases of biogenic origin may be an approach to detect the presence of microbial life on the surface or subsurface of Mars. Chemical thermodynamic calculations indicate that on both Earth and Mars, certain gases should exist in extremely low concentrations, if at all. Microbial metabolic activity is an important non-equilibrium chemistry process on Earth, and if microbial life exists on Mars, may be an important nonequilibrium chemistry process on Mars. The non-equilibrium chemistry of the atmosphere of Mars is discussed in this paper.
    Keywords: Exobiology
    Type: Sixth International Conference on Mars; LPI-Contrib-1164
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  • 5
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    A two-stage mechanism for escape of Na and K from Io (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A two-stage process is presented to identify Io as the source of Na and K ions in the Io plasma torus. The Voyager I IRIS experiment recorded an SO2 abundance of 0.2 cm atm in the Io subsolar region, and further calculations determined that the S(+) and O(+) would have sufficient energy to penetrate the Io atmosphere and produce sputtering of surface atoms at a rate of 800 million/sq cm per sec. If K, Na, and S are present on the surface in cosmic proportions, then an evenly applied sputter distribution would produce the same abundances of sputtered Na and K as observed in the Na and K clouds around Io. Sputtered into the atmosphere, the ions undergo thermal Jean's escape and attain velocities of at least 2.6 km/sec. The sputtering ions are a factor of two greater on the Jupiter side than on the solar side, in agreement with asymmetries measured by the Voyager.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 304; Aug. 25
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  • 6
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    The structure of Io's thermal corona and implications for atmospheric escape (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A steady-state model of Io's exospheric corona and its interaction with the Io plasma torus is used to study the escape of species from Io's atmosphere. It is found that atmospheric sputtering is the major escape mechanism for models in which the plasma flow reaches the critical level, and that such models produce total mass-loading rates an order of magnitude larger than values inferred from observations. The results suggest the presence of an extended Na coronal component in the thermal exosphere, and are consistent with an O-dominated corona, an exospheric temperature of about 1000 K, an Na critical level mixing ratio of 0.001, and a critical level radius of about 1.5 Io radii.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 343; 468-480
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  • 7
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    Methane on Mars: Thermodynamic Equilibrium and Photochemical Calculations (2010)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: The detection of methane (CH4) in the atmosphere of Mars by Mars Express and Earth-based spectroscopy is very surprising, very puzzling, and very intriguing. On Earth, about 90% of atmospheric ozone is produced by living systems. A major question concerning methane on Mars is its origin - biological or geological. Thermodynamic equilibrium calculations indicated that methane cannot be produced by atmospheric chemical/photochemical reactions. Thermodynamic equilibrium calculations for three gases, methane, ammonia (NH3) and nitrous oxide (N2O) in the Earth s atmosphere are summarized in Table 1. The calculations indicate that these three gases should not exist in the Earth s atmosphere. Yet they do, with methane, ammonia and nitrous oxide enhanced 139, 50 and 12 orders of magnitude above their calculated thermodynamic equilibrium concentration due to the impact of life! Thermodynamic equilibrium calculations have been performed for the same three gases in the atmosphere of Mars based on the assumed composition of the Mars atmosphere shown in Table 2. The calculated thermodynamic equilibrium concentrations of the same three gases in the atmosphere of Mars is shown in Table 3. Clearly, based on thermodynamic equilibrium calculations, methane should not be present in the atmosphere of Mars, but it is in concentrations approaching 30 ppbv from three distinct regions on Mars.
    Keywords: Geosciences (General)
    Type: NF1676L-9951 , Astrobiology Science Conference 2010. Evolution and Life: Surviving Catastrophes and Extremes on Earth and Beyond; Apr 26, 2010 - Apr 29, 2010; League City, TX; United States
    Format: application/pdf
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  • 8
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    The ionosphere of Triton (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A model of the atmospheric temperature structure and composition inferred from the Voyager (UVS) solar occultations was used together with a one-dimensional chemical diffusive model to interpret the Voyager Radio Science Spectrometer (RSS) ingress measurements of Triton's electron density. Although N2(+) is the major ion created, N(+) produced by dissociative ionization is the dominant ion. Reaction of thermospheric H2, produced by Lyman-alpha dissociation of CH4 in the lower atmosphere, is the major loss for N(+) ions and maintains these ions in PCSS below 600 km. Solar EUV ionization cannot generate electron densities at the magnitude measured by the RSS experiment and an additional ionization source about 3 x 10 to the 8th ions/sq cm per sec is required. The ionosphere may undergo a transition from PCSS to diffusive control if the N(+) ion production rates were greater than the H2 flux derived from CH4. In this case, the upward flowing H2 is totally converted to H by reaction with N(+) and the remaining N(+) ions recombine radiatively to create an ionosphere under diffusive control above the peak.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1721-172
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  • 9
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    Detection of neutral oxygen and sulfur emissions near Io using IUE (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: IUE spectra have shown several O I and S I emissions near Io. The optical thickness of the S I 1814 A multiplet indicates that the S column density is greater than about 2 x 10 to the 12th/sq cm. The presence of an S I 1479 A feature suggests that electron collisions with SO2 could be a major source of the emissions. It is likely that particle excitation in the denser collision-dominated part of the atmosphere is also responsible for a substantial part of the observed emissions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 319; L33-L38
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  • 10
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    The Formation of Charon's Red Poles from Seasonally Cold-Trapped Volatiles (2016)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A unique feature of Plutos large satellite Charon is its dark red northern polar cap. Similar colours on Plutos surface have been attributed to tholin-like organic macromolecules produced by energetic radiation processing of hydrocarbons. The polar location on Charon implicates the temperature extremes that result from Charons high obliquity and long seasons in the production of this material. The escape of Pluto's atmosphere provides a potential feedstock for a complex chemistry. Gas from Pluto that is transiently cold-trapped and processed at Charon's winter pole was proposed as an explanation for the dark coloration on the basis of an image of Charon's northern hemisphere, but not modelled quantitatively. Here we report images of the southern hemisphere illuminated by Pluto-shine and also images taken during the approach phase that show the northern polar cap over a range of longitudes. We model the surface thermal environment on Charon and the supply and temporary cold-trapping of material escaping from Pluto, as well as the photolytic processing of this material into more complex and less volatile molecules while cold-trapped. The model results are consistent with the proposed mechanism for producing the observed colour pattern on Charon.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN40508 , Nature (ISSN 0028-0836) (e-ISSN 1476-4687); 539; 7627; 65-68
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