Biology
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p24a..05s&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P24A-05
Biology
[0750] Cryosphere / Sea Ice, [5200] Planetary Sciences: Astrobiology, [5422] Planetary Sciences: Solid Surface Planets / Ices, [6221] Planetary Sciences: Solar System Objects / Europa
Scientific paper
Historically one of the most studied and yet least constrained of Europa’s terrains, chaos regions are likely indicators of a geologically active ice shell. Chaos terrain is generally characterized by broken ice “raft” relicts of the former surface embayed by a dark, hummocky matrix rich in non-ice material. Chaos features, though they bear resemblance to broken-up terrestrial sea-ice, are generally topographically higher than the surrounding plains. Interior to these features topographic variation can also be found. From a geophysical perspective, chaos terrain may offer the possibility to test models for Europa’s ice shell thickness, its rheological properties, and its dynamics, since they occur ubiquitously across the surface. The existence of chaos terrain has, in the past, been used to suggest that either the shell is thin, and thus large-scale melt-through events have taken place to create chaos, or that the shell is actively convecting, and thus that the chaos terrain is formed by diapirism associated with rising plumes. Partial melt and the movement of warm ice have also been suggested to contribute to the formation of chaos. While these formation models are strongly tied to an ice thickness assumption, it is agreed that the break-up of ice and the subsequent motion of the blocks is suggestive of a material that has been free to flow at some point; the nature of the “fluidization” has not been discovered. In terrestrial marine ice sheets, brine infiltration is known to occur in porous layers called firn that are formed by annual accretion of snow. At the seaward edge of the sheet, or through tidally-formed basal cracks, sea water can percolate inward through the porous layer and travel kilometers from the source. In the McMurdo Ice shelf, brine extends radially through the ice to 10’s of km from the source at the shelf edge. In the Larsen ice shelf, a brine-laden layer of ice exists that does not reach the seaward edge, arguing that infiltration has instead occurred from basal cracks. Brine infiltration occurs even at many degrees below the freezing point of the embaying brine. We have undertaken a study of how brine infiltration may operate on Europa and contribute to the formation of chaos terrain. Rising plumes within the shell may not be sufficient to melt or break the ice, however pressure melt driven by rising ice may promote the collection of enriched brines at the heads of plumes. If such activity can cause small scale cracks to form in the brittle lithospheric layer of Europa’s ice shell overlying large plumes, brines may percolate into the multiply fractured and porous upper ice. The fluid can then both break up existing, denser blocks and destroy more brittle regions, allowing for the formation of a matrix enhanced in non-ice materials while preserving blocks and allowing them to move. Such a process may explain the height of, as well as topographic variability within, chaos terrain. Our goal is to establish how orbital lidar and radar sounding observations of chaos terrain may be used to evaluate hypothesized ice shell properties and ice-ocean exchange processes.
Blankenship Donald D.
Schmidt Britney Elyce
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