Abstract: Modeling and Assessing Transpressional Tectonics on Europa through General Shear

A glimpse at the frozen surface of Europa

A glimpse at the frozen surface of Europa

In the outer solar system, large planets have accrued a sum of moons which orbit them and vary in size from only a few kilometers across to roughly the size of the Earth’s moon. The four largest and most recognizable moons of Jupiter are Ganymede, Io, Callisto, and Europa, “discovered” by Galileo in 1610 with a primitive telescope. My research advisors, Professor Chuck Bailey from the Geology Department of William & Mary in Williamsburg, Virginia and Dr. Jon Kay from the Lunar and Planetary Institute in Houston, Texas, find the moon Europa particularly interesting. Europa is characterized by a crust of ice above a liquid water ocean twice the volume of all the water on Earth, both of which are above a silicate mantle and metallic core. This icy crust exhibits a range of morphologies from cross-cutting faults and lineaments to short ridges to chaotic terrains to bands of shearing from strike slip motions. What is relatively lacking at the surface, as compared to other bodies without much of an atmosphere, is a plethora of craters. Indeed, most planetary scientist tend to date surfaces by analyzing the crater density we observe. However, Europa has very few craters, leading to an estimated surface age of only 40-100 million years old. Imagine if Earth was that young at the surface! No dinosaurs older than the Late Cretaceous would ever have been found! Also, the majority of the structures seen at the surface appear to be strike slip or extensional in nature. That would imply that the moon is continuously growing in size, yet over decades of observation the surface area of the moon has stayed the same. How can this be? I suspect that there may be transpression, a combination of compression and transform motion, in the icy shell of Europa. It is my hypothesis that at certain transform boundaries, faults, folds, and lineaments accommodate strain as general shear, a telling sign that transpression could be at play. Over the course of the summer, I will investigate my hypothesis by using photography of Europa at a regional scale (a few hundred thousand square kilometers) to create a tectonic reconstruction to model the kinematics of how icy blocks of Europa’s crust moved to make the current surface. Then, I will calculate expected stress from the movement of the icy blocks and predict some elements of general shear that I expect to see at the surface. Consequently, I will investigate photography at a more local scale (hundreds of square kilometers) to determine if observed features match my expectations. If you have any questions, feel free to email me at grdenny@email.wm.edu for clarifications and explanations.

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