Erin Leonard
Regional geomorphologic map of a region on Europa from Leonard et al. (2018) 

Regional geomorphologic map of a region on Europa from Leonard et al. (2018) 

Planetary Mapping

Geomorphologic Mapping

I create detailed maps of surface features on icy satellites, mostly Europa and Enceladus, at the highest resolution available. This is not commonly practiced on Europa especially because less than 0.03% of Europa’s surface was imaged at resolution <50 m/pixel and not practiced in general due to the immense complexity of these icy surfaces. The purpose of these maps is to aid me in analyzing potential surface feature formation mechanisms and create an inferred evolutionary sequence. For example, my geomorphological map of Europa’s E12 Mottle Region highlights texture and details, such as slope symmetry, spacing and cross-sectional shape. These observed characteristics now become requirements for the formation mechanism. Creating geomorphologic maps can also provide insight into the potential similarities and differences of surface features across icy satellites.

Structural Analysis

Using the observations gained from Geomorphologic Mapping, I hypothesize formation mechanisms for the different surface features or structures. I then analyze the formation mechanism, its viability in the environment, and its potential implications. Different formation mechanisms can have different implications for the thickness of the ice shell, rheology, or other values like heat flux, at least at the time when the structures were formed. An example of this is my work on the Crater Islands on Enceladus (see Publications).

Image Processing

I have created many mosaics with images from the Galileo mission, obtained from the Planetary Data System (PDS), using the USGS program ISIS3. The Europa mosaics are used in my work as well as others, including Alyssa Rhoden’s students at ASU. Examples of these mosaics can be seen in my Europa High-Resolution Mapping papers (see publications).

Stereo Topography

In order to squeeze as much information out of the Galileo images of Europa as possible, I also create stereo topography where possible using the AMES Stereopipline software. Some of these topographic products are made under ideal conditions (large change in emission angle, or the angle the image was taken from), but others I create to try and extract information from non-ideal pairs. For example, the E12 Mottle images from the Galileo SSI are separated only by tenths of a degrees in emission angle, but the topography I made from the image overlaps still holds valuable information.


Analogue Experiments

Lab Work

The existence of global oceans on icy satellites, such as Europa and Enceladus, implies the presence of a ductile warm ice layer because there must be some transition from the brittle ice surface to the subsurface global ocean. The role of a ductile layer has only been explored with infinitesimal strain computer models to date (i.e., Bland and McKinnon, 2012; Dombard and McKinnon, 2006), which does not address potential finite (>1) strain icy satellites experience. I aim to address this issue by combining my mapping (Part 1) with a unique two-layer analogue model containing an overlying brittle layer and a ductile creeping layer. Although analogue models have been widely used for tectonic studies on Earth (i.e., Cruz et al., 2008; Maillot and Koyi, 2004; Davy and Cobbold, 1988), they have only rarely been adapted to the studies of the icy-surface deformation (cf., Sims et al., 2014; Manga and Sinton, 2004). I plan to expand on the previous analogue experimental studies by having multiple rheological layers—an underlying ductile and an overlying brittle layer—using materials that will properly scale up to the icy satellites, following Hubbert (1937).

The analogue experiments consist of a ductile, low-viscosity layer underlying a cohesive brittle layer. I will use therapeutic putty with a measured viscosity of about 104 Pa s for the ductile layer and fine-grained sand (~100 mm) for the brittle layer. I chose these materials for the experiments because they will scale up reasonably to conditions on Europa and Enceladus