True polar wander on Europa from global-scale small-circle depressions

Abstract

The tectonic patterns and stress history of Europa are exceedingly complex1 and many large-scale features remain unexplained. True polar wander, involving reorientation of Europa’s floating outer ice shell about the tidal axis with Jupiter, has been proposed2 as a possible explanation for some of the features. This mechanism is possible if the icy shell is latitudinally variable in thickness and decoupled from the rocky interior. It would impose high stress levels on the shell, leading to predictable fracture patterns3. No satisfactory match to global-scale features has hitherto been found for polar wander stress patterns3. Here we describe broad arcuate troughs and depressions on Europa that do not fit other proposed stress mechanisms in their current position. Using imaging from three spacecraft, we have mapped two global-scale organized concentric antipodal sets of arcuate troughs up to hundreds of kilometres long and 300 m to 1.5 km deep. An excellent match to these features is found with stresses caused by an episode of 80° true polar wander. These depressions also appear to be geographically related to other large-scale bright and dark lineaments4,5, suggesting that many of Europa’s tectonic patterns may also be related to true polar wander.

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Figure 1: Regional views of global-scale arcuate troughs and basins on Europa.
Figure 2: A global map of the distribution of large-scale arcuate troughs and basins on Europa.
Figure 3: Highest-resolution image mosaic of a large secondary basin on Europa.
Figure 4: Global colour mosaic and predicted stress patterns for true polar wander in a thin elastic shell on Europa.

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Acknowledgements

This work was supported in part by the NASA Outer Planets Research and Planetary Geology and Geophysics programmes. LPI contribution no. 1399.

Author Contributions Global mapping and topographic analyses were conducted by P.S.; P.S. and F.N. conducted preliminary examination of alternative models; numerical modelling of stress patterns was conducted by I.M.; and P.S wrote the paper, with contributions from I.M. and F.N.

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Correspondence to Paul Schenk.

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Schenk, P., Matsuyama, I. & Nimmo, F. True polar wander on Europa from global-scale small-circle depressions. Nature 453, 368–371 (2008) doi:10.1038/nature06911

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