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E.P. Turtle (Univ. of Arizona), T.V. Johnson (JPL), P. Thomas (Cornell Univ.), T. Denk (Freie Univ., Berlin), B. Giese (DLR), J.C. Castillo, D.L. Matson (JPL), P. Helfenstein (Cornell)
The topography exhibited on the surface of icy satellites provides important clues to the internal structural and thermal conditions of those bodies. Although their surface temperatures are generally too cold to allow the ice to deform significantly (even at planet-sized scales) over the lifetime of the Solar System, depending on the interior thermal gradient (and history thereof) the deeper ice can be warm enough to deform over geologic timescales. Intriguingly, while 1490-km-diameter Iapetus appears to have undergone very little viscous relaxation (e.g., Giese et al. 2005; Denk et al. 2005; Porco et al. 2005; Castillo et al. 2005), the surface of 500-km-diameter Enceladus exhibits significant evidence for such processes (e.g., Passey 1983; Helfenstein et al. 2005).
Finite-element models incorporating parameters for water ice (e.g., Durham et al. 1997) and model thermal gradients (e.g., Ellsworth and Schubert 1983; Castillo et al. 2005) and constrained by Iapetus' topography, e.g. its several large impact basins (Giese et al. 2005), high equatorial ridge (Porco et al. 2005; Denk et al. 2005), and its current global shape, which is consistent with an early, rapid-rotation state (Castillo et al. 2005), demonstrate that the lithosphere needs to be relatively thick and cold to have supported the observed basin topography and global shape over timescales of billions of years. On the other hand, in order for the ridge to be built, a thinner, more mobile lithosphere is likely required. Therefore, these structures may put tight temporal constraints on Iapetus' history.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.