Forming Iapetus' Equatorial Ridge

Details Forming Iapetus' Equatorial Ridge Forming Iapetus' Equatorial Ridge

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusm.p33a..04m&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P33A-04

Mathematics

Logic

5430 Interiors (8147), 5450 Orbital And Rotational Dynamics (1221), 6280 Saturnian Satellites, 8005 Folds And Folding, 8020 Mechanics, Theory, And Modeling

Scientific paper

A close flyby of Iapetus by the Cassini spacecraft on December 31, 2004 revealed the presence of a ridge (~250 km wide), 15 to 20 km high, located exactly at the equator. Crater counting indicates that the ridge is as old as its surroundings (Giese et al. BAAS 37, 2005). This indicates the formation of this feature early in Iapetus' history. Its location at the equator might hold the key to its origin. It has been proposed that the ridge might have been an outcome of Iapetus' despinning to synchronous rotation (Denk et al. LPSC 36, 2005). We investigate this assumption by evaluating the evolution of Iapetus' shape as a function of spin period. We present coupled thermal-dynamical models differing in their initial conditions (e.g., composition of volatiles, presence of short-lived radiogenic species, porosity). One of these models includes short-lived radiogenic species in such a way to account for both Iapetus' present dynamical state and rotational bulge preservation until present (e.g., Castillo et al. BAAS 37, 2005) For each case we evaluate (a) the evolution of the mechanical lithospheric thickness as a function of time; (b) the redistribution of material as a function of spin period evolution (i.e., resulting from equatorial radius decrease and polar radius increase); (c) the different stresses developing during this period due to thermal evolution, change in dynamical state, porosity decrease. We show that early despinning triggered by the effect of short-lived radiogenic species is favorable to the production of excess material at the equator, while the lithosphere is thin enough to be deformed, but thick enough to preserve the ridge in the long run. We argue that similar early geological history might have taken place on other satellites. This work was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract.

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