Robert Pappalardo
Jet Propulsion Lab. (JPL), California Inst. Technology (Caltech) (Pasadena, California, Etats-Unis d'Amérique)
Other ridge and trough terrains and related landforms also occur on Io, Europa, Callisto, Enceladus, Tethys, Dione, Rhea, Miranda, Ariel, and Triton. A variety of geological processes can produce individual ridge or trough landforms or sets of ridge and trough terrain. In tectonic models, they can be produced by extension (as tilt-block or horst-and-graben normal fault blocks), contraction (as thrust blocks and/or folds), or strike-slip (especially as related to fault duplexing. In magmatic models, ridges might form by extrusion (as linear eruptions) or intrusion (as linear laccolith-like bodies) of volcanic or diapiric source materials.
Imaging data from the Voyager, Galileo, and Cassini spacecraft reveal a wide variety of specific ridge and trough morphologies on the outer planet satellites. Extensional tectonism is inferred as the principal cause of many ridge and trough terrains, and has tectonically resurfaced older terrains at least partially by erasing preexisting features and/or brightened surfaces by revealing brighter material beneath a darker surface layer (on Ganymede, Europa, Enceladus, Tethys, Dione, and Rhea). There is also strong evidence that contraction (on Io, Europa, and Enceladus) and strike-slip faulting (on Ganymede and Europa) have shaped some ridge and trough terrains. Active strike-slip tectonism is inferred on Enceladus today, driven by tidal forcing as the satellite orbits Saturn. Intrusive and extrusive models are viable for some individual ridge and ridge sets on Europa, Miranda, Ariel, and Triton.
While important commonalities of morphologies and process exist, multiple processes are inferred to have formed ridges and troughs on the outer planet satellites, implying rich geological histories.
Salle des séminaires Évry Schatzman, Institut d'Astrophysique de Paris