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Formation of metre-scale bladed roughness on Europa’s surface by ablation of ice

Matters Arising to this article was published on 02 December 2019

An Author Correction to this article was published on 13 November 2019

This article has been updated

Abstract

On Earth, the sublimation of massive ice deposits at equatorial latitudes under cold and dry conditions in the absence of any liquid melt leads to the formation of spiked and bladed textures eroded into the surface of the ice. These sublimation-sculpted blades are known as penitentes. For this process to take place on another planet, the ice must be sufficiently volatile to sublimate under surface conditions and diffusive processes that act to smooth the topography must operate more slowly. Here we calculate sublimation rates of water ice across the surface of Jupiter’s moon Europa. We find that surface sublimation rates exceed those of erosion by space weathering processes in Europa’s equatorial belt (latitudes below 23°), and that conditions would favour penitente growth. We estimate that penitentes on Europa could reach 15 m in depth with a spacing of 7.5 m near the equator, on average, if they were to have developed across the interval permitted by Europa’s mean surface age. Although available images of Europa have insufficient resolution to detect surface roughness at the multi-metre scale, radar and thermal data are consistent with our interpretation. We suggest that penitentes could pose a hazard to a future lander on Europa.

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Fig. 1: Terrestrial penitentes from the southern end of the Chajnantor plain, Chile.
Fig. 2: Modelled variation in rates of surface sublimation, and equivalent total depth of ice removal, with Europan latitude.
Fig. 3: Remote sensing evidence consistent with an equatorial band of penitentes on Europa.

Data availability

The data that support the findings of this study are available on the NASA Planetary Data System (PDS) (https://pds.nasa.gov/).

Change history

  • 13 November 2019

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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Acknowledgements

We thank D. Blankenship, K. Mitchell, F. Nimmo and G. Tucker, and especially J. Spencer for discussions that shaped the form of this paper. Funding was from the Europa Pre-Project Mission Concept Study via the Jet Propulsion Laboratory, California Institute of Technology. We are grateful to P. Engebretson for contribution to figure production. We thank C. Chavez for her help with manuscript preparation.

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D.E.J.H. compiled data, performed and interpreted numerical analyses, and wrote the bulk of the paper. J.M.M. conceived and designed the study and organized the revision of the manuscript. A.D.H. was involved in the study, design, interpretation, and revision. Both J.M.M. and A.D.H. performed preliminary analyses. O.M.U. significantly revised the numerical analyses found in the Methods section. All authors discussed the results and commented on the manuscript.

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Correspondence to Daniel E. J. Hobley.

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Hobley, D.E.J., Moore, J.M., Howard, A.D. et al. Formation of metre-scale bladed roughness on Europa’s surface by ablation of ice. Nature Geosci 11, 901–904 (2018). https://doi.org/10.1038/s41561-018-0235-0

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