Other
Scientific paper
Feb 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997icar..125..380p&link_type=abstract
Icarus, Volume 125, Issue 2, pp. 380-396.
Other
12
Scientific paper
We model the time- and longitude-dependent charged particle absorption signatures caused by solid body absorbers, such as icy satellites, in Saturn's magnetosphere. The reduction in particle density caused by passage of such an absorber through a magnetic flux tube is calculated numerically. We then solve numerically for the time- and space-dependent distribution of particles in phase space assuming transport by radial diffusion and longitudinal particle drifts. The fully time- and longitude- averaged solution of the lossy radial diffusion equation is assumed to be the initial state, and the calculation is performed for up to a few complete satellite orbital periods. In this way, we obtain a numerical solution for the effects of particle absorption and transport during the most recent orbit(s) of the absorbing body around Saturn, while we approximate the result of all previous orbits of the absorber with the fully relaxed, steady state solution. We define ``high'' and ``low'' diffusion rates, depending on whether the diffusive fill-in of the absorption wake is fast or slow compared to the time before the satellite re-encounters its wake. For two cases, using parameters appropriate for the low energy charged particle (LECP) instruments on the Voyager spacecraft, we simulate count rate profiles where microsignatures have been observed. In the case of an ion microsignature near Enceladus, we cannot reproduce the data using radial diffusion rates inferred by other studies. For an electron microsignature very close to Tethys, we do find that the simulated count rate profile has a deep enough minimum that it could be detected by the Voyager instrument. In some cases, observed ion microsignatures are deeper than the maximum possible depth predicted by our model for a fresh absorption signature immediately downstream of a moon, assuming high diffusion. In the low diffusion case, our model predicts deeper signatures, sufficient to account for observed microsignatures. However, in that case, the fully relaxed solution contains dramatic changes in the initial phase space density and furthermore we would then expect microsignatures to be observed at every satellite L-shell crossing, which is not the case.
Cheng Andrew F.
Paranicas Chris
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