Other
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..672c&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Other
Scientific paper
We have carried out test-particle simulations of the ejection of sodium atoms from the icy matrix of Europa. Sodium atoms are ejected from the surface by both magnetospheric ions and electrons sputtering and desorption stimulated by UV solar photons. Variations of the emission of sodium in the exosphere of Europa during its orbit around Jupiter are investigated. The comparative study of sputtering and PSD ejection processes tend to indicate than PSD alone can not account for the emission variations reported by [1]. A minimal surface source term of Sodium of 3x106cm-2.s-1 is required to produce the average emission intensities observed at different positions around Jupiter, in good agreement with [2]. The spatial distribution of the ejected material does not significantly influence the averaged emission variability at high altitudes (typically larger than 4000km) along Europa's orbit for a uniform Na surface source term distribution. At altitudes typically lower than 500km, however, the surface content produce clear asymmetries of the exospheric density from trailing to leading hemispheres. Temporal variation of the impacting flux intensity and especially local plasma injection may also drive large emission variability. In particular, we estimate that a global increase of the flux of particles impacting the surface by a factor of 8 compared to the ambient energetic ions and electrons flux during 10 hours would be sufficient to explain the enhanced emission observed on the 11/29/2000 [1]. A similar enhancement should be expected for the other components of Europa's atmosphere. Therefore, any observation of Europa's atmosphere and more generally of any Jovian sattelites need to be correlated with observations of the activity occurring in the parent planet magnetosphere. In another way, these transient events occurring at the Jovian satellites will represent key situations when surface properties and composition should be derived from atmospheric measurements.
Cipriani Fabio
Johnson Robert E.
LeBlanc Francis
Witasse Olivier
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