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The topography of Iapetus' leading side

Giese, Bernd and Denk, Tilmann and Neukum, Gerhard and Roatsch, Thomas and Helfenstein, Paul and Thomas, Peter and Turtle, Elizabeth and McEwen, Alfred and Porco, Carolyn (2008) The topography of Iapetus' leading side. Icarus, 193 (2), pp. 359-371. Elsevier. DOI: 10.1016/j.icarus.2007.06.005. ISSN 0019-1035.

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Abstract

We have used Cassini stereo images to study the topography of Iapetus' leading side. A terrain model derived at resolutions of 4-8 km reveals that Iapetus has substantial topography with heights in the range of -10 km to +13 km, much more than observed on the other middle-sized satellites of Saturn so far. Most of the topography is older than 4 Ga (Neukum et al., 2005) which implies that Iapetus must have had a thick lithosphere early in its history to support this topography. Models of lithospheric deflection by topographic loads provide an estimate of the required elastic thickness in the range of 50-100 km. Iapetus' prominent equatorial ridge (Porco et al., 2005) reaches widths of 70 km and heights of up to 13 km from their base within the modeled area. The morphology of the ridge suggests an endogenous origin rather than a formation by collisional accretion of a ring remnant (Ip, 2006). The transition from simple to complex central peak craters on Iapetus occurs at diameters of 11±3 km. The central peaks have pronounced conical shapes with flanking slopes of typically 11° and heights that can rise above the surrounding plains. Crater depths seem to be systematically lower on Iapetus than on similarly sized Rhea, which if true, may be related to more pronounced crater-wall slumping (which widens the craters) on Iapetus than on Rhea. There are seven large impact basins with complex morphologies including central peak massifs and terraced walls, the largest one reaches 800 km in diameter and has rim topography of up to 10 km. Generally, no rings are observed with the basins consistent with a thick lithosphere but still thin enough to allow for viscous relaxation of the basin floors, which is inferred from crater depth-to-diameter measurements. In particular, a 400-km basin shows up-domed floor topography which is suggestive of viscous relaxation. A model of complex crater formation with a viscoplastic (Bingham) rheology (Melosh, 1989) of the impact-shocked icy material provides an estimate of the effective cohesion / viscosity at 0.04±0.01 MPa / 0.6±0.2 GPas. The local distribution of bright and dark material on the surface of Iapetus is largely controlled by topography and consistent with the dark material being a sublimation lag deposit originating from a bright icy substrate mixed with the dark components, but frost deposits are possible as well.

Document Type:Article
Title:The topography of Iapetus' leading side
Authors:
AuthorsInstitution or Email of Authors
Giese, BerndUNSPECIFIED
Denk, TilmannFreie Universität Berlin
Neukum, GerhardFreie Universität Berlin
Roatsch, ThomasUNSPECIFIED
Helfenstein, PaulCornell University, Ithaca, USA
Thomas, PeterCornell University, Ithaca, USA
Turtle, ElizabethJohns Hopkins University, Laurel, USA
McEwen, AlfredUniversity of Arizona, Tucson, USA
Porco, CarolynSpace Science Institute, Boulder, USA
Date:2008
Journal or Publication Title:Icarus
Refereed publication:Yes
In ISI Web of Science:Yes
Volume:193
DOI:10.1016/j.icarus.2007.06.005
Page Range:pp. 359-371
Publisher:Elsevier
ISSN:0019-1035
Status:Published
Keywords:Iapetus, Saturn satellites, Craters
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EW - Erforschung des Weltraums
DLR - Research area:Space
DLR - Program:W EW - Erforschung des Weltraums
DLR - Research theme (Project):W - Vorhaben CASSINI (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Geodesy
Deposited By: Dr.rer.nat. Bernd Giese
Deposited On:15 Jan 2008
Last Modified:27 Apr 2009 14:18

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