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Impact gardening on Europa and repercussions for possible biosignatures

Nature Astronomy volume 5, pages 951–956 (2021)Cite this article

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Abstract

Owing to its internal ocean, Jupiter’s moon Europa can potentially host extant life. However, because Europa’s orbit is within Jupiter’s magnetosphere, chemical biosignatures that are exposed to space may be destroyed by high-energy electron radiation. It has been suggested that biosignatures may be preserved below the radiation-penetration depth of the top few centimetres. Impact gardening, the process by which small impacts mechanically churn the uppermost surface of airless bodies, is known to disrupt near-surface stratigraphy; however, no comprehensive estimate of the effect of gardening has yet been determined for Europa. Here we use an impact gardening model to show that gardening is a global process on Europa, and has churned, on average, the top 30 cm over the last several tens of millions of years, thus, exposing all material within the top 30 cm to surface radiation. We suggest that morphologically immature craters and regions of mass wasting at mid-to-high latitudes could be weakly impacted by both gardening and radiation, and should be preferred locations for the search for life on Europa.

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Fig. 1: The impact rate at Europa.
Fig. 2: Modelled impact gardening.
Fig. 3: Gardening by region.

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Data availability

All the impact gardening results reported can be reproduced using the equations and parameters provided in this paper. We reference parameters for scaling impactor diameter to crater diameter from table 1 of Costello et al.17. We also reference impact flux information available in Zahnle et al.29, radiation flux information from Nordheim et al.7 and crater size–frequency distributions reported in Bierhaus et al.15,26,27. Source data are provided with this paper.

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Acknowledgements

This work was supported and facilitated by a summer internship with the National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL) Summer Internship Program and by a NASA Solar System Workings Program grant to the University of Hawaii (grant number 6107932: ‘An Analytic Model for Impact Gardening Across the Solar System’; to E.S.C., R.R.G. and P.G.L.). E.S.C. and C.B.P. were partially funded by the Europa Lander Mission Concept at JPL.

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Authors and Affiliations

  1. Hawaiʻi Institute of Geophysics and Planetology, Honolulu, HI, USA

    E. S. Costello & P. G. Lucey

  2. Department of Earth & Planetary Sciences, University of Hawaiʻi at Mānoa, Honolulu, HI, USA

    E. S. Costello & P. G. Lucey

  3. NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    C. B. Phillips

  4. Planetary Science Institute, Tucson, AZ, USA

    R. R. Ghent

Authors
  1. E. S. Costello
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  2. C. B. Phillips
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  3. P. G. Lucey
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  4. R. R. Ghent
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Contributions

E.S.C. was the primary contributor to the development of the model described in this work, produced the figures, performed the scientific analysis and wrote the manuscript. C.B.P. contributed to the formulation of the scientific question addressed in this work, the scientific analysis, and the editing and revision of the manuscript. R.R.G. contributed to the model development and execution and to the editing and revision of the manuscript. P.G.L. contributed by securing the funding that supported this work, by assisting in model development, and to the editing and revision of the manuscript.

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Correspondence to E. S. Costello.

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The authors declare no competing interests.

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Peer review information Nature Astronomy thanks Mihaly Horanyi, Micah Schaible and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Source data

Source Data Fig. 1

Cumulative crater count data and model solutions to reproduce the plot in Fig. 1.

Source Data Fig. 2

Impact gardening model results as a function of probability, including cumulative Poisson distribution values for λ, and gardening calculations as a function of time.

Source Data Fig. 3

Impact gardening results as a function of probability using the Bierhaus et al. crater counts.

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Costello, E.S., Phillips, C.B., Lucey, P.G. et al. Impact gardening on Europa and repercussions for possible biosignatures. Nat Astron 5, 951–956 (2021). https://doi.org/10.1038/s41550-021-01393-1

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