1.  学术报告：Orbital constraints on the internal structures of Enceladus and Dione | | When：Dec. 11, 10:00am
Where: Room 1514 (教学行政楼)
Who: Dr. Ke Zhang from UC Santa Cruz
Abstract.
Due to their close distance to Saturn, the giant planet raises
strong tides on its inner icy satellites. In the case of Enceladus,
tidal dissipation has been a major conceivable contribution to its
excessive heat outflow. The strength of tidally-generated heat flow
depends on the interior structure of the satellite, e.g., whether it
possesses an ocean, or whether heat is transferred conductively or
convectively in the ice shell. The energy source of tidal heating,
however, is ultimately Enceladus' orbital energy. As a satellite's
body is tidally deformed, its orbit is altered, and energy is
transferred during the process. As so, we can use orbital evolution
to constrain the satellite's internal structure. It is
much easier and less expensive to observe satellites' orbits than
probe their interior directly. In fact, for most of the icy
satellites in the outer Solar System, direct probe is not an option at
all.
In this study, we focus on the orbital behavior of Enceladus and
Dione during their passage through the 2:1 mean-motion resonances, and
constrain their interior structures parameterized by the tidal Love
number and the tidal dissipation factor. Assuming Maxwellian
viscoelastic behavior, we find that for Enceladus a convective ice
shell overlying an ocean is too dissipative to match the orbital
constraints, while a conductive shell without ocean is not
dissipative enough. We conclude that a conductive shell overlying an
ocean is more likely. Dione's ice shell is also likely to be
conductive, but our results are less constraining.
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