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@ARTICLE{Simon:824031,
author = {Simon, Sven and Kriegel, Hendrik and Saur, Joachim and
Wennmacher, Alexandre and Neubauer, Fritz M. and Roussos,
Elias and Motschmann, Uwe and Dougherty, Michele K.},
title = {{A}nalysis of {C}assini magnetic field observations over
the poles of {R}hea},
journal = {Journal of geophysical research},
volume = {117},
number = {A7},
issn = {0148-0227},
address = {Washington, DC},
publisher = {Union91972},
reportid = {FZJ-2016-06657},
pages = {A07211},
year = {2012},
abstract = {We analyze Cassini magnetic field observations from the
only two polar flybys of Saturn's largest icy satellite Rhea
(R2 on 02 March 2010 and R3 on 11 January 2011) which are
scheduled between Saturn Orbit Insertion and the end of the
mission in 2017. For the interpretation of these data, we
apply estimations from simple analytical models as well as
results from numerical hybrid simulations (kinetic ions,
fluid electrons) of Rhea's interaction with the incident
magnetospheric plasma. In-situ observations of exospheric
neutral gas and pick-up ions suggest Rhea to be embedded in
a tenuous gas envelope. However, the interaction of this gas
with the magnetospheric flow does not make any measurable
contributions to the magnetic field perturbations detected
above the poles of the moon. Instead, the field
perturbations observed in these regions mainly arise from
the absorption of magnetospheric particles with large
field-aligned velocities, impinging on the north and south
polar surface of Rhea. In addition to numerous interaction
features known from preceding Cassini flybys of Saturn's
plasma-absorbing moons, the magnetic field data acquired
above Rhea's poles reveal perturbations of the flow-aligned
field component, corresponding to a draping/Alfvén wing
pattern. Based on our hybrid simulations, we suggest that
these signatures arise from the finite extension of Rhea's
wakeside plasma void along the corotational flow direction,
yielding a density gradient in corotation direction, and
thereby generating a diamagnetic current from the
Saturn-facing into the Saturn-averted hemisphere of the
moon. This transverse current is responsible for generating
a weak Alfvén wing pattern at Rhea which has been detected
by the Cassini spacecraft during the R2 and R3 flybys. Due
to the large gyroradii of the incident magnetospheric ions,
this structure features a pronounced asymmetry with respect
to the direction of the convective electric field. Results
of our simulation, considering only plasma absorption on the
moon, are in good agreement with Cassini magnetometer data
from both flybys. At Saturn's icy satellites Tethys and
Dione, the low value of the magnetospheric plasma beta most
likely prevents the formation of similar currents and
measurable flow-aligned magnetic field distortions.},
cin = {NIC},
ddc = {550},
cid = {I:(DE-Juel1)NIC-20090406},
pnm = {899 - ohne Topic (POF3-899) / Plasma and Dust Simulations
on the Saturnian Rings $(hbs06_20111101)$},
pid = {G:(DE-HGF)POF3-899 / $G:(DE-Juel1)hbs06_20111101$},
typ = {PUB:(DE-HGF)16},
UT = {WOS:000306701600005},
doi = {10.1029/2012JA017747},
url = {https://juser.fz-juelich.de/record/824031},
}