RIDGES OF ENCELADUS, EUROPA, AND OTHER ICY WORLDS

Many icy satellites of the outer solar system show signs of either ongoing geologic activity or an extended period of deformation after the moon was formed. The history of activity is commonly preserved in the form of ridge and trough terrains. Ridges can display different morphological forms including a single or double ridge, ridge complex, or a ridge plain, can stand from 10s to ~1000 m high, reach widths of 2–20 kilometers, and reach over a thousand kilometers in length. Ridge and trough terrains can be found on moons of each of the outer solar system's planets, but the nature of their formation appears to be varied and complex. These features can preserve past periods of extension, contraction, and/or shearing and may help to determine the thickness and constitutive properties of the upper-most portions of the icy shell. Here, we expand on previous geological mapping of ridges on icy satellites and focus on those found on Enceladus and Europa, to constrain whether the ridges are related to one another in terms of their structure, evolution, and implied formation mechanisms. We create geological maps to assist in the classification of ridge types by comparing basic characteristics, such as planform shape, cross-sectional shape, length, height, width, and slope. The mapping can also identify common geological associations, as well as crosscutting relationships that are used to determine the relative ages of ridges. Ridges that are similar from one moon to the next invite consideration of analogous formation mechanisms. For example, the “tiger stripe” double ridges of the Enceladus South Polar Terrain resemble double ridges on Europa, and are potentially analogous to features observed on Neptune’s moon Triton. The morphological similarities and differences among ridges on different icy satellites will help to constrain the tectonic and volcanic histories of the moons and could help to determine if the moons experienced similar evolutionary paths.