Preservation of potential biosignatures in the shallow subsurface of Europa

Abstract

Jupiter’s moon Europa, which is thought to possess a large liquid water ocean beneath its icy crust, is one of the most compelling targets in the search for life beyond Earth. Its geologically young surface, along with a number of surface features, indicate that material from Europa’s interior may be emplaced on the surface. However, the surface is affected by the harsh radiation environment of Jupiter’s magnetosphere, which over time may lead to chemical alteration and destruction of potential biosignatures. We show that radiation dose rates are highly dependent on surface location. Radiation processing and destruction of potential biosignatures is found to be significant down to depths of ~1 cm in mid- to high-latitude regions, and to depths of 10–20 cm within ‘radiation lenses’ centred on the leading and trailing hemispheres. These results indicate that future missions to Europa’s surface do not need to excavate material to great depths to investigate the composition of endogenic material and search for potential biosignatures.

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Fig. 1: Energetic electron bombardment patterns for the surface of Europa.
Fig. 2: Representative electron and proton particle flux spectra at Europa.
Fig. 3: Timescales for the accumulation of a significant radiation dose at different depths for several locations on the surface of Europa.
Fig. 4: Radiation processing map of Europa’s surface.
Fig. 5: Destruction of amino acids within Europa surface material for young and old surface material.

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Acknowledgements

T.A.N. was supported by an appointment to the NASA Postdoctoral Fellowship Program at the Jet Propulsion Laboratory administered by Oak Ridge Associated Universities and Universities Space Research Association through a contract with NASA. K.P.H. acknowledges support from the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. T.A.N. and K.P.H. acknowledge the support of the Cassini Data Analysis Program (NNN13D466T).

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T.A.N. carried out the modelling of energetic electron and proton interactions at the surface of Europa as well as calculation of amino acid destruction rates. C.P. provided fit functions for the electron and proton spectra at Europa as well as guidance on the modelling of energetic electron access to Europa’s surface. K.P.H. provided overall guidance on the execution of the research as well as providing key inputs on the discussion of biosignature destruction at Europa. All authors contributed to the writing of the manuscript.

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Correspondence to T. A. Nordheim.

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Nordheim, T.A., Hand, K.P. & Paranicas, C. Preservation of potential biosignatures in the shallow subsurface of Europa. Nat Astron 2, 673–679 (2018). https://doi.org/10.1038/s41550-018-0499-8

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