Mechanisms for the Production of Energetic Atomic Hydrogen from Dissociation of Molecular Hydrogen on Saturn

Details Mechanisms for the Production of Energetic Atomic Hydrogen from Dissociation of Molecular Hydrogen on Saturn Mechanisms for the Production of Energetic Atomic Hydrogen from Dissociation of Molecular Hydrogen on Saturn

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p11b1233l&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P11B-1233

Physics

[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [0358] Atmospheric Composition And Structure / Thermosphere: Energy Deposition, [2756] Magnetospheric Physics / Planetary Magnetospheres, [6275] Planetary Sciences: Solar System Objects / Saturn

Scientific paper

Images of atomic hydrogen Lyman-α emission in the Saturn atmosphere and magnetosphere obtained with the Cassini UVIS far ultraviolet spectrograph have shown the escape of H atoms from the top of the thermosphere. An image at 0.1 × 0.1 Saturn equatorial radii (RS) pixel resolution with an edge-on-view of the rings shows a distinctive plume structure with FWHM of 0.56 RS at the exobase sub-solar limb at ~ -13.5° latitude as part of the distributed out flow of H atoms from the sunlit hemisphere, with a counter-part on the anti-solar side peaking near the equator above the exobase limb. The structure of the image indicates that part of the out flowing population is sub-orbital and re-enters the thermosphere in ~ 5 hour time scale. An evident larger more broadly distributed component fills the magnetosphere to beyond 45 RS in the orbital plane in an asymmetric distribution in local time. H2 singlet-ungerade Rydberg extreme and far ultraviolet emission spectra collected with the H Lyman-α into the image mosaic show a distinctive resonance property correlated with the H Lyman-α plume. The inferred approximate globally averaged energy deposition at the top of the thermosphere from the production of the hot atomic hydrogen accounts for the measured atmospheric temperature. Possible processes for the fast atomic hydrogen formation from dissociation of H2 include the excitation of singlet-ungerade states and doubly excited states by photons and electrons, and the excitation of the singlet-gerade and triplet states by electrons, and chemical reactions involving the formation and dissociative recombination of H3+. Based on the available laboratory measurements and quantum mechanics calculations, the assessment of various mechanisms for H2 → H production, especially those producing H atoms with sufficient energy to escape from Saturn, will be presented.

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