Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p41a1256o&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P41A-1256
Other
0343 Planetary Atmospheres (5210, 5405, 5704), 2431 Ionosphere/Magnetosphere Interactions (2736), 2732 Magnetosphere Interactions With Satellites And Rings, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
We have studied the low-energy (5-100 eV) electron-induced degradation of low temperature ice characteristic of icy Jovian satellite surfaces. Specifically, we examined the yields and energy distributions of the primary neutral and cationic fragments leaving the surface as a function of impinging electron energy, ice phase and surface temperature. We find a large proton yield and formation and desorption of H (2S) and H2 (^{1}Σg+). These neutrals were detected using laser resonance enhanced multi-photon ionization. The threshold electron energy is 6.5 eV and the energy distributions of the desorption products are non-thermal indicating surface exciton decay. Proton production and release has a threshold energy of 22 eV and involves two-hole states which Coulomb explode. Other desorption products include O (3P), O (1D) and O2. The formation of O2 is enhanced in porous media and involves a molecular precursor. The overall cross sections for producing the above mentioned products, particularly O2, increase as the ice temperature rises from 90 to 150 K. This is due to the increased excited state lifetimes associated with the disrupted hydrogen bonding network at elevated temperatures and enhanced precursor formation at temperatures above 120 K. In general, the yields of protons are high enough to provide a significant source of ions to the near space environments of Jupiter's icy moons and potentially to the Jovian magnetosphere. In the case of direct proton ejection, this source term may be as effective as hydrogen atom emission followed by gas-phase ionization. No oxygen ions are emitted from the ice due to the high solvation forces. These results, in conjunction with modeling studies of Ganymede's magnetospheric interaction with the Jovian magnetosphere, indicate that oxygen ions are likely present in Ganymede's ionosphere and magnetosphere.
Alexandrov Alexander
Grieves G.
Orlando Thomas M.
Paty Carol
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