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Energetic Ion and Electron Irradiation of the Icy Galilean SatellitesGalileo Orbiter measurements of energetic ions (20 keV to 100 MeV) and electrons (20-700 keV) in Jupiter's magnetosphere are used, in conjunction with the JPL electron model (less than 40 MeV), to compute irradiation effects in the surface layers of Europa, Ganymede, and Callisto. Significant elemental modifications are produced on unshielded surfaces to approximately centimeter depths in times of less than or equal to 10(exp 6) years, whereas micrometer depths on Europa are fully processed in approximately 10 years. Most observations of surface composition are limited to optical depths of approximately 1 mm, which are indirect contact with the space environment. Incident flux modeling includes Stormer deflection by the Ganymede dipole magnetic field, likely variable over that satellite's irradiation history. Delivered energy flux of approximately 8 x 10(exp 10) keV/square cm-s at Europa is comparable to total internal heat flux in the same units from tidal and radiogenic sources, while exceeding that for solar UV energies (greater than 6 eV) relevant to ice chemistry. Particle energy fluxes to Ganymede's equator and Callisto are similar at approximately 2-3 x 10(exp 8) keV/square cm-s with 5 x 10(exp 9) at Ganymede's polar cap, the latter being comparable to radiogenic energy input. Rates of change in optical reflectance and molecular composition on Europa, and on Ganymede's polar cap, are strongly driven by energy from irradiation, even in relatively young regions. Irradiation of nonice materials can produce SO2 and CO2, detected on Callisto and Europa, and simple to complex hydrocarbons. Iogenic neutral atoms and meteoroids deliver negligible energy approximately 10(exp 4-5) keV/square cm-s but impacts of the latter are important for burial or removal of irradiation products. Downward transport of radiation produced oxidants and hydrocarbons could deliver significant chemical energy into the satellite interiors for astrobiological evolution in putative sub-surface oceans.
Document ID
20010125134
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Cooper, John F.
(Raytheon Information Technology and Scientific Services Greenbelt, MD United States)
Johnson, Robert E.
(Virginia Univ. Charlottesville, VA United States)
Mauk, Barry H.
(Johns Hopkins Univ. Laurel, MD United States)
Garrett, Henry B.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Gehrels, Neil
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
August 20, 2013
Publication Date
January 1, 2001
Publication Information
Publication: Icarus
Publisher: Academic Press
Volume: 149
ISSN: 0019-1035
Subject Category
Lunar And Planetary Science And Exploration
Funding Number(s)
CONTRACT_GRANT: NASW-99029
CONTRACT_GRANT: NAS5-98156
CONTRACT_GRANT: NAS5-97059
Distribution Limits
Public
Copyright
Other

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