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  • 1985-1989  (8)
  • 1
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    Monte Carlo Particle Trajectory Models for Neutral Cometary Gases. II. The Spatial Morphology of the Lyman-Alpha Coma (1988)
    Institute of Physics
    Details
    Publication Date: 1988-04-01
    Print ISSN: 0004-637X
    Electronic ISSN: 1538-4357
    Topics: Physics
    Published by Institute of Physics
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    PAPER CURRENT
  • 2
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    Correlating east-west asymmetries in the Jovian magnetosphere and the Io sodium cloud (1987)
    American Geophysical Union
    Details
    Publication Date: 1987-09-01
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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    PAPER CURRENT
  • 3
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    The role of hydrogen thermalization in shaping the Lyman-alpha coma (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two interrelated aspects of the thermalization of cometary hydrogen were addressed using a three-dimensional Monte Carlo particle trajectory model: photochemical heating of the coma and the velocity distribution of cometary hydrogen leaving the inner coma that produces the extended Lyman-alpha coma. Observed cometary conditions were examined, ranging from productive comets like Kohoutek at very small heliocentric distances to intrinsically small comets like Giacobini-Zinner at 1 AU. The collisional decoupling of hydrogen yields bulk flow speeds and gas temperatures which are smaller than generally predicted in hydrodynamic models. By properly including these conditions the hydrogen velocity distribution required to produce the observed Lyman-alpha coma can be derived naturally. The two-dimensional morphology of the H coma is diagnostic of the physical conditions in the inner coma.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: ESA, Proceedings of the International Symposium on the Diversity and Similarity of Comets; p 621-626
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    A modeling analysis program for the JPL table mountain Io sodium cloud data (1988)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Research in the third and final year of this project is divided into three main areas: (1) completion of data processing and calibration for 34 of the 1981 Region B/C images, selected from the massive JPL sodium cloud data set; (2) identification and examination of the basic features and observed changes in the morphological characteristics of the sodium cloud images; and (3) successful physical interpretation of these basic features and observed changes using the highly developed numerical sodium cloud model at AER. The modeling analysis has led to a number of definite conclusions regarding the local structure of Io's atmosphere, the gas escape mechanism at Io, and the presence of an east-west electric field and a System III longitudinal asymmetry in the plasma torus. Large scale stability, as well as some smaller scale time variability for both the sodium cloud and the structure of the plasma torus over a several year time period are also discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-182555 , NAS 1.26:182555
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Extended atmospheres of outer planet satellites and comets (1988)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: In the third year of this 3-year project, research accomplishments are discussed and related to the overall objective. In the area of the distribution of hydrogen in the Saturn system, new Voyager UVS data have been discovered and are discussed. The data suggest that both Titan's hydrogen torus and Saturn's hydrogen corona play a major role in the circumplanetary gas source. Modeling analysis of this new data establishes a strong basis for continuing studies to be undertaken in a new NASA-sponsored project. In the area of the cometary atmospheres, observational data for H, O, C, and OH acquired with the Pioneer Venus Orbiter are evaluated and preliminary modeling analysis for some of the hydrogen Lyman-alpha data is presented. In addition, the importance of collisional thermalization in spatial properties and structure of the inner and extended comae of comets has been demonstrated using the recently developed particle trajectory model. The successful simulation by this model of the hydrogen Lyman-alpha image for Comet Kohoutec near perihelion, an extreme case for collisional thermalization, is particularly noteworthy.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-183157 , NAS 1.26:183157
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Extended atmospheres of outer planet satellites and comets (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A major model documentation paper for cometary gas coronae and a second paper successfully applied the model to simulate the hydrogen Lyman-alpha coma of comet Kohoutek were completed and are discussed. New and very exciting data for the hydrogen distribution in the Saturn system obtained form earlier unreduced Voyager 1 and Voyager 2 data are preliminarily reviewed. This new data opens up a whole new series of investigations and indicate that Saturn's corona plays a major role in supplying hydrogen to the circumplanetary volume.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-181449 , NAS 1.26:181449
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Monte Carlo particle-trajectory models for neutral cometary gases. I - Models and equations. II - The spatial morphology of the Lyman-alpha coma (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The mathematical derivations of various methods employed in the Monte Carlo particle-trajectory model (MCPTM) are presented, and the application of the MCPTM to the calculation of the photochemical heating of the inner coma through the partial thermalization of cometary hydrogen atoms produced by the photodissociation of water is discussed. This model is then used to explain the observed morphology of the spatially extended Ly-alpha comas of comets. The rocket and Skylab images of the Ly-alpha coma of Comet Kohoutek are examined.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 327; 1026-105
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Correlating east-west asymmetries in the Jovian magnetosphere and the Io sodium cloud (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Three east-west intensity asymmetries in the Jupiter system that would appear to an earth observer in optical S+, extreme ultraviolet S++ and optical Na emissions are reviewed. The three asymmetries imply that some combination of the plasma torus number densities and electron temperature is, on the long-term average, larger west of Jupiter than east of Jupiter. A small east-to-west electric field, previously proposed to explain the ion intensity asymmetries, is also shown to provide a natural explanation for the sodium intensity asymmetry. A long-term average east-to-west electric field of about 3 mV/m and a corresponding west-to-east offset of about 0.16 Jupiter radii for the plasma torus at Io's orbital distance are implied. On a shorter time scale, the east-west electric field appears to be time variable and may be readily monitored from earth by observations of the sodium cloud.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 14; 973-976
    Format: text
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