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Laboratory predictions for the night-side surface ice glow of Europa

Nature Astronomy volume 5, pages 276–282 (2021)Cite this article

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15 June 2021 Editor's Note: The authors have informed the editors of Nature Astronomy about an error in converting the laboratory electron simulated emission data to the number of photons reaching the Wide Angle Camera pixels. The authors are working to better quantify those numbers, but in the meantime, readers are cautioned against using the paper’s estimate. Interested readers may contact the corresponding author for further information.

Abstract

Europa’s surface continuously experiences high fluxes of charged particles due to the presence of Jupiter’s strong magnetic field. These high-energy charged particles, including electrons, interact with the ice- and salt-rich surface, resulting in complex physical and chemical processes. Here, we report that Europa ice analogues emit characteristic spectral signatures in the visible region when exposed to high-energy electron radiation. The strongest emission (ice glow) we observed was centred at ~525 nm. We found that the presence of sodium chloride and carbonate strongly quenched, while epsomite enhanced, the radiation-induced ice glow. These emission characteristics could be used to determine the chemical composition of Europa’s surface during night-time low-altitude fly-bys of spacecraft such as the Europa Clipper. We estimate that the Europa Clipper Wide Angle Camera could record between 500 and 280,000 counts per second through different colour filters, depending on the chemical composition of Europa’s surface. Though we focus here on Europa, our study may be relevant to other bodies exposed to high doses of ionizing radiation, such as Io and Ganymede. With its extreme radiation environment, rich surface geology and compositional diversity, the radiation-induced ice glow on Europa could enable more precise surface characterization and provide unique night-time views.

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Fig. 1: Visible light emission from a crystalline water-ice core cooled to 100 K by liquid nitrogen flow as it was being irradiated by 10.5 MeV electrons.
Fig. 2: Electron energy and flux dependence of water ice luminescence under simulated Europa surface conditions.
Fig. 3: MeV electron-induced ice glow from salty ice surfaces.
Fig. 4: Effect of temperature on electron-induced emission from water ice.
Fig. 5: Estimates of signals to be detected by the WAC pixels from Europa’s surface ice glow based on analogue laboratory studies.

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Data availability

The data that support the figures and table within this paper and other findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

Change history

  • 15 June 2021

    Editor's Note: The authors have informed the editors of Nature Astronomy about an error in converting the laboratory electron simulated emission data to the number of photons reaching the Wide Angle Camera pixels. The authors are working to better quantify those numbers, but in the meantime, readers are cautioned against using the paper’s estimate. Interested readers may contact the corresponding author for further information.

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Acknowledgements

This work was supported by JPL’s internal R&TD funds as well as funding from NASA Solar System Workings and Habitable Worlds Programs. Experiments were performed at the NIST and data analysed at JPL. This work was conducted by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Certain commercial equipment is identified in this paper to adequately describe the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology or the Jet Propulsion Laboratory, California Institute of Technology.

Author information

Authors and Affiliations

  1. Science Division, NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    Murthy S. Gudipati & Bryana L. Henderson

  2. National Institute of Standards and Technology, Gaithersburg, MD, USA

    Fred B. Bateman

Authors
  1. Murthy S. Gudipati
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  2. Bryana L. Henderson
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  3. Fred B. Bateman
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Contributions

M.S.G. conceived the idea. M.S.G. and B.L.H. conducted the experimental work at NIST. B.L.H. and M.S.G. conducted the data analysis. M.S.G. and B.L.H. wrote the manuscript. F.B.B. provided experimental support, beam operations and monitoring of the electron flux.

Corresponding author

Correspondence to Murthy S. Gudipati.

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The authors declare no competing interests.

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Peer review information Nature Astronomy thanks Timothy Cassidy and Anna Pollmann for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 An example of an original raw emission spectrum (red line) showing spikes caused by the high-energy MeV electron radiation environment in spite of shielding by lead bricks.

These spikes are effectively removed by percentile filter option in the Origin Labs plotting program. Processed spectrum is shown below the raw spectrum (black line). Spectra are displaced along y-axis for visibility.

Source data

Supplementary information

Supplementary Data 1

Describes computational steps to convert lab data into counts per second at the WAC, estimates of aurorae counts.

Source data

Source Data Fig. 2

Raw data, normalization, smoothing and calibrations.

Source Data Fig. 3

Ascii data.

Source Data Fig. 4

Raw data, normalization, smoothing and calibrations.

Source Data Fig. 5

Ascii data.

Source Data Extended Data Fig. 1

Ascii data.

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Gudipati, M.S., Henderson, B.L. & Bateman, F.B. Laboratory predictions for the night-side surface ice glow of Europa. Nat Astron 5, 276–282 (2021). https://doi.org/10.1038/s41550-020-01248-1

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