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Long-term & large-scale viscous evolution of dense planetary rings | | Julien Salmon
; Sébastien Charnoz
; Aurélien Crida
; André Brahic
; | | Date: |
3 Jun 2010 | | Abstract: | We investigate the long-term and large-scale viscous evolution of dense
planetary rings using a simple 1D numerical code. We use a physically realistic
model derived from N-body simulations (Daisaka et al., 2001), and dependent on
the disk’s local properties (surface mass density, particle size, distance to
the planet). Particularly, we include the effects of gravitational
instabilities (wakes) that importantly enhance the disk’s viscosity. We show
that common estimates of the disk’s spreading time-scales with constant
viscosity significantly underestimate the rings’ lifetime. With a realistic
viscosity model, an initially narrow ring undergoes two successive evolutionary
stages: (1) a transient rapid spreading when the disk is self-gravitating, with
the formation of a density peak inward and an outer region marginally
gravitationally stable, and with an emptying time-scale proportional to 1/M_0^2
(where M_0 is the disk’s initial mass) (2) an asymptotic regime where the
spreading rate continuously slows down as larger parts of the disk become
not-self-gravitating due to the decrease of the surface density, until the disk
becomes completely not-self-gravitating. At this point its evolution
dramatically slows down, with an emptying time-scale proportional to 1/M_0,
which significantly increases the disk’s lifetime compared to the case with
constant viscosity. We show also that the disk’s width scales like t^{1/4} with
the realistic viscosity model, while it scales like t^{1/2} in the case of
constant viscosity, resulting in much larger evolutionary time-scales in our
model. We find however that the present shape of Saturn’s rings looks like a
100 million-years old disk in our simulations. Concerning Jupiter’s, Uranus’
and Neptune’s rings that are faint today, it is not likely that they were much
more massive in the past and lost most of their mass due to viscous spreading
alone. | | Source: | arXiv, 1006.0633 | | Services: | Forum | Review | PDF | Favorites | |
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