July 9, 2014
Tectonic-Like Stretching Forces Shaped Ganymede’s Surface
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Jupiter's moon Ganymede is the largest satellite in our solar system, approximately three-quarters the size of Mars. Ganymede has two types of terrain on the surface: highly cratered dark regions comprising nearly 40 percent of the surface, with the rest being lightly grooved in intricate patterns.
A new study, led by researchers with the Southwest Research Institute (SwRI), reveals that the processes which shaped these ridges and troughs is likely similar to tectonic processes observed on Earth.
The findings, reported in Geophysical Research Letters, are the result of subjecting physical models made of clay to stretching forces that simulate tectonic action. By using such physical analog models in laboratory settings, the scientists are able to study the developmental sequence of various phenomena as they occur.
The research team was comprised of scientists from SwRI, NASA's Jet Propulsion Laboratory (JPL), Wheaton College and NuStar Energy LP. Using the models, they devised complex patterns of faults that are similar to the ridge and trough features — called grooved terrain — observed in some regions of Ganymede. The "wet clay cake" material of the models has brittle characteristics that simulate how the ice moon's lithosphere (the outermost solid shell) responds to stresses by cracking.
The reaction of the clay models to the stressors indicates that the grooved terrain is a result of the surface being stretched.
“The physical models showed a marked similarity to the surface features observed on Ganymede,” said Dr. Danielle Wyrick, a senior research scientist in the SwRI Space Science and Engineering Division. “From the experiments, it appears that a process in which the crust breaks into separate blocks by large amounts of extension is the primary mechanism for creating these distinct features.”
“Physical analog modeling allows us to simulate the formation of complex three-dimensional geologic structures on Ganymede, without actually going to Ganymede,” said Dr. David Ferrill, director of the Earth, Material and Planetary Sciences Department in the SwRI Geosciences and Engineering Division. “These scaled models are able to reproduce the fine geometric details of geologic processes, such as faulting, and to develop and test hypotheses for landscape evolution on planetary bodies.”
Physical analog models have been used by the SwRI researchers in the past to examine the processes that form pit craters on Mars, and how magma within the Martian subsurface deforms the outer surface.
Image 2 (below): An image of a tabletop-size analog model (left) shows details of fault systems created by extension that visually match an image by spacecraft Galileo of faulted terrain on Ganymede (right). Credit: Left Image: Courtesy of Southwest Research Institute; Right Image: Courtesy of NASA/JPL SSI image s0552443639
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