Chaotic Terrain on Europa

Abstract

Chaotic terrain covers approximately one-quarter of Europa's surface, and is formed by disruption of the preexisting surface into isolated plates, and formation of lumpy matrix material between the plates. Key observations include the motion of plates of preexisting terrain within chaos areas, the matrix material commonly elevated above the background terrain, associated dark hydrated materials exposed at the surface, concentration into two antipodal areas around the equator, and a large and continuous range of different sizes and morphologies. Of the models that have been proposed to explain chaotic terrain formation, a melt-through model and a brinemobilization model best fit the observations. The melt-through model faces serious energy problems, while some details of the brine-mobilization model lack sufficient quantification. None of the existing models offer a completely satisfactory explanation for chaos formation yet, but future data from an orbiting spacecraft could decisively test the hypotheses.

Europa’s disk-resolved ultraviolet spectra: Relationships with plasma flux and surface terrains

“…A variety of smaller disruptions known as lenticulae pepper the surface. The origin of these features is unclear (e.g., Collins and Nimmo, 2009;Prockter and Patterson, 2009), but may be related to the presence of a subsurface ocean (Pappalardo et al, 1999) and may involve the delivery of ocean water (or other subsurface material) to the surface, including sulfur (Zolotov et al, 2009) or sodium (e.g., Leblanc et al, 2005) compounds. Hydrated sulfuric acid has been found to be associated with these geologic terrains (e.g., Carlson et al, 1999a), and SO 2 absorption has shown some correlation with the hydrate concentration (Hendrix et al, 2002) on the anti-jovian hemisphere.…”

SPATIALLY RESOLVED SPECTROSCOPY OF EUROPA’S LARGE-SCALE COMPOSITIONAL UNITS AT 3–4 μm WITH KECK NIRSPEC

“…The geographic distribution of surface species is important because it can reveal endogenous or exogenous sources through association with geologic or external processes. One key target for such observations is large-scale chaos, young regions of widely disrupted terrain indicating interaction with the subsurface (e.g., Lucchitta & Soderblom 1982;Carr et al 1998;Collins & Nimmo 2009). Chaos regions are likely the most direct link to the subsurface environment and endogenous composition.…”

Observational constraints on the identification and distribution of chaotic terrain on icy satellites

“…A variety of hypotheses have been proposed to explain chaos formation based on observed surface morphology and inferred subsurface structure (e.g., Pappalardo et al, 1998;Greenberg et al, 1999;Cox et al, 2008;Schmidt et al, 2011). A leading hypothesis suggests that chaos results from thermal or compositional upwelling of ice diapirs producing near surface brines (Collins and Nimmo, 2009;Schmidt et al, 2011), but the exact formation mechanism is still not well understood. Nonetheless, it seems likely that chaos is a significant mechanism by which material is transported from the subsurface to the surface of Europa, and is therefore important in understanding the interior structure and heat transport of Europa at the present time.…”

“…Regions of chaos appear as disrupted areas of Europa's surface, consisting of plates of pre-existing crustal material surrounded by a lumpy matrix (e.g., Collins and Nimmo, 2009). Chaotic terrain ranges in size from $1 to 100,000 km 2 (Riley et al, 2000;Spaun, 2002), and the matrix commonly (though not always) exhibits a dark, reddish-brown color that has been attributed to radiolysis of surface materials producing reddish sulfur compounds (Carlson et al, 2002).…”