Geologic mapping of Europa

Abstract

Abstract. Galileo data enable the major geological units, structures, and surface features to be identified on Europa. These include five primary units (plains, chaos, band, ridge, and crater materials) and their subunits, along with various tectonic structures such as faults. Plains units are the most widespread. Ridged plains material spans a wide range of geological ages, including the oldest recognizable features on Europa, and appears to represent a style of tectonic resurfacing, rather than cryovolcanism. Smooth plains material typically embays other terrains and units, possibly as a type of fluid emplacement, and is among the youngest material units observed. At global scales, plains are typically mapped as undifferentiated plains material, although in some areas differences can be discerned in the near infrared which might be related to differences in ice grain size. Chaos material is composed of plains and other preexisting materials that have been severely disrupted by inferred internal activity; chaos is characterized by blocks of icy material set in a hummocky matrix. Band material is arrayed in linear, curvilinear, wedge-shaped, or cuspate zones with contrasting albedo and surface textures with respect to the surrounding terrain.

Nonsynchronous Rotation Evidence and Fracture History in the Bright Plains Region, Europa

“…Fractures within the boundaries of the mapped area do not exceed lengths of ∼12 km and some are segmented, forming en echelon geometries. Many of the fractures appear to form wide crevasses at the surface, referred to as troughs by Greeley et al (2000). Surface fractures formed in response to near-surface tension and are interpreted to not extend deep enough into the Europan crust to tap an underlying liquid ocean, assuming one exists.…”

“…Fracture lineaments and other geological features were characterized using a classification scheme modified after those of Prockter et al (1999a), Figueredo and Greeley (2000), and Greeley et al (2000). Numerous conceptual models have been developed to explain the evolution of and relationships between the various fracture lineaments (Geissler et al 1998b, Kadel et al 1998, Pappalardo et al 1998b.…”

Large-scale doming on Europa: A model of formation of Thera Macula

“…However, Voyager and more recently Galileo's images reveal a surface widely disturbed by "geological" features (Lucchitta and Soderblom, 1982;Greeley et al, 2000;Figueredo and Greeley, 2000). These observations suggest that processes have driven movements in the icy crust in the past and possibly recently and have refreshed the surface 1999;Mével and Mercier, 2005).…”

Europa's dynamic icy crust

“…Impressions that chaos is systematically younger than tectonic terrain (Prockter et a!., 1999;Greeley et al, 2000) are probably artifacts of this observational bias. No evidence has yet been developed for any systematic change over time in frequency or style of chaos formation.…”

“…From Voyager images, such terrain was characterized as "bright plains", because the ridges were too fine to see at low resolution. Galileo mapping called it "background plains" (e.g., Prockter et al, 1999;Figueredo and Greeley, 2000) reflecting an assumption that this is the oldest type of terrain on Europa (Greeley et aI., 2000). That terminology might suggest an initial slate-cleaning event.…”