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Spatial distribution of ice blocks on Enceladus and implications for their origin and emplacement

Martens, Hilary R. and Ingersoll, Andrew P. and Ewald, Shawn P. and Helfenstein, Paul and Giese, Bernd (2015) Spatial distribution of ice blocks on Enceladus and implications for their origin and emplacement. Icarus, 245 . pp. 162-176. ISSN 0019-1035. https://resolver.caltech.edu/CaltechAUTHORS:20150105-102816930

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Abstract

We have mapped the locations of over 100,000 ice blocks across the south polar region of Saturn’s moon Enceladus, thus generating the first quantitative estimates of ice-block number density distribution in relation to major geological features. Ice blocks were manually identified and mapped from twenty of the highest resolution (4–25 m per pixel) Cassini Imaging Science Subsystem (ISS) narrow-angle images using ArcGIS software. The 10–100 m-diameter positive-relief features are marginally visible at the resolution of the images, making ice-block identifications difficult but not impossible. Our preliminary results reveal that ice blocks in the southern hemisphere are systematically most concentrated within the geologically active South Polar Terrain (SPT) and exhibit peak concentrations within 20 km of the tiger-stripe fractures as well as close to the south pole. We find that ice blocks are concentrated just as heavily between tiger-stripe fractures as on the directly adjacent margins; although significant local fluctuations in ice-block number density do occur, we observe no clear pattern with respect to the tiger stripes or jet sources. We examine possible roles of several mechanisms for ice-block origin, emplacement, and evolution: impact cratering, ejection from fissures during cryovolcanic eruptions, tectonic disruption of lithospheric ice, mass wasting, seismic disturbance, and vapor condensation around icy fumeroles. We conclude that impact cratering as well as mass wasting, perhaps triggered by seismic events, cannot account for a majority of ice-block features within the inner SPT. The pervasiveness of fracturing at many size scales, the ubiquity of ice blocks in the inner SPT, as well as the occurrence of linear block arrangements that parallel through-cutting crack networks along the flanks of tiger stripes indicate that tectonic deformation is an important source of blocky-ice features in the SPT. Ejection during catastrophic cryovolcanic eruptions and condensation around surface vents, however, cannot be ruled out. Further, sublimation processes likely erode and disaggregate ice blocks from solid exposures of ice, especially near the warm tiger-stripe fractures. The relative paucity of blocks beyond the bounds of the SPT, particularly on stratigraphically old cratered terrains, may be explained in part by mantling of the surface by fine particulate ice grains that accumulate over time.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.icarus.2014.09.035 DOIArticle
http://www.sciencedirect.com/science/article/pii/S0019103514005016PublisherArticle
ORCID:
AuthorORCID
Ingersoll, Andrew P.0000-0002-2035-9198
Additional Information:© 2014 Elsevier Inc. Received 3 July 2014; Revised 15 September 2014; Accepted 17 September 2014; Available online 11 October 2014. We thank Alex Hayes and Antoine Lucas for valuable guidance in image processing using ISIS and mapping using ArcGIS. Alex Hayes graciously provided additional utility code for reading and processing ISIS files within Matlab. We are also grateful for the insightful and helpful comments raised by two anonymous reviewers. This manuscript is based upon work supported by the National Science Foundation Graduate Research Fellowship to H.R. Martens under Grant No. DGE-1144469. P. Helfenstein gratefully acknowledges support from NASA CDAP Grant NNX12AG82G.
Funders:
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1144469
NASANNX12AG82G
Subject Keywords:Enceladus; Satellites, surfaces; Geological processes; Ices
Record Number:CaltechAUTHORS:20150105-102816930
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20150105-102816930
Official Citation:Hilary R. Martens, Andrew P. Ingersoll, Shawn P. Ewald, Paul Helfenstein, Bernd Giese, Spatial distribution of ice blocks on Enceladus and implications for their origin and emplacement, Icarus, Volume 245, 1 January 2015, Pages 162-176, ISSN 0019-1035, http://dx.doi.org/10.1016/j.icarus.2014.09.035. (http://www.sciencedirect.com/science/article/pii/S0019103514005016)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:53171
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:06 Jan 2015 19:31
Last Modified:03 Oct 2019 07:47

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