Ongoing activity at Enceladus: A search Through Time

Goals and Objectives.

Saturn’s small ice-covered moon Enceladus was first viewed in high resolution by the Voyager 1 and 2 spacecraft in 1980 and 1981, respectively. Roughly a quarter century later, the Cassini spacecraft began imaging the icy world at an even higher resolution. These missions revealed a surprisingly youthful surface and eventually provided evidence for present-day geyser-like activity on the satellite. For this proposal, we aim to determine if Enceladus experienced any detectable geological changes between the Voyager era and Cassini’s arrival in the Saturn system, or at any time during the Cassini mission. We seek to constrain if any geological changes, such as the growth of a fracture or the movement of a ridge, are visible on the surface of Enceladus. We also seek to determine if the moon’s icy shell experienced any motion due to nonsynchronous rotation (NSR), or true polar wander (TPW). The relatively long gap between Voyager images and Cassini, and the nearly 13 years Cassini spent in orbit around Saturn, may be enough to find differences between the data sets. If no changes or evidence for motion are found, we will still be able to set a lower limit on the modern period of NSR and an upper limit on the rate of geologic resurfacing. If changes are observed, it would be the first documentation of geological changes on an airless icy satellite and provide a crucial input for crater rate models, surface age determinations, and/or the tectonic and stress history of Enceladus. For this study we have 2 major objectives:

Objective 1: Determine if any surface geological changes occurred between the time of the Voyager images and the Cassini mission, or during the Cassini mission.
Objective 2: Determine if Enceladus experienced any nonsynchronous rotation or true polar wander between the time of the Voyager images and the Cassini mission.

Approach and Methodology.

This work will use Cassini Imaging Science Subsystem (ISS) images and Voyager ISS images. First, we will select appropriate image pairs for comparison. We will compare Cassini images to the same regions imaged by Voyager, for Cassini-Voyager image pairs. Additionally, we will use Cassini images of the same areas but taken at different times and analyze them for differences. We will match Cassini-Voyager and Cassini-Cassini image pairs as closely as possible in resolution, filter, and viewing and lighting geometry. We will first coregister and reproject each image pair, and then make precise measurements of observable surface features to look for changes in the size, shape, or brightness of features due to geologic activity, or changes in absolute feature location in a way consistent with NSR or TPW.