| Autor: |
Howard Todd Smith, Donald G. Mitchell, Robert E. Johnson, Barry H. Mauk, Jacob E. Smith |
| Předmět: |
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| Zdroj: |
Astrophysical Journal; 1/20/2019, Vol. 871 Issue 1, p1-1, 1p |
| Abstrakt: |
The confirmation and constraints of a Europa-generated neutral torus are presented based on available observations and computational modeling of relevant source species. These results are applied to determine if the Energetic Neutral Atom (ENA) images reported by Mauk et al. were produced by interactions with a Europa neutral particle torus or with the local charged particle population. Neutral tori provide important insights into the processes operating in large planet magnetospheres. Such features emerge when particles escape an embedded satellite and form a population that co-orbits with the moon. Torus distributions and compositions are directly related to the satellite composition and source mechanisms. Significant findings are as follows. (1) The presence of a Europa neutral torus is confirmed through the development of 3D Io and Europa neutral tori models. (2) Density constraints for H, H2, O, and O2 in the Europa neutral torus are determined. (3) The torus is highly asymmetric: Near Europa, ∼99% of the ENA image is produced by the neutral torus. Furthest from Europa, ∼15%–69% of the ENA emissions are caused by charge exchange interaction within the ambient plasma. In addition, we showed that (4) 7%–34% of the ENAs near Europa would be produced by charge exchange with neutrals, even with a three order of magnitude neutral source rate reduction (<2 × 1024). (5) Satellite source rate variations take longer to impact the Europa neutral torus than the Io neutral torus. Dominant processes at Europa’s orbit have lifetimes >2–8 days, while at Io, the neutral particles lifetimes are as short as 8–13 hr. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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