Letter

Nature 453, 368-371 (15 May 2008) | doi:10.1038/nature06911; Received 18 July 2007; Accepted 6 March 2008

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

Paul Schenk1, Isamu Matsuyama2 & Francis Nimmo3

  1. Lunar and Planetary Institute, Houston, Texas 77058, USA
  2. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20015, USA
  3. Department of Earth & Planetary Sciences, University of California, Santa Cruz, California 95064, USA

Correspondence to: Paul Schenk1 Correspondence and requests for materials should be addressed to P.S. (Email: schenk@lpi.usra.edu).

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 approx1.5 km deep. An excellent match to these features is found with stresses caused by an episode of approx80° 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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