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Evidence of a plume on Europa from Galileo magnetic and plasma wave signatures


The icy surface of Jupiter’s moon, Europa, is thought to lie on top of a global ocean1,2,3,4. Signatures in some Hubble Space Telescope images have been associated with putative water plumes rising above Europa’s surface5,6, providing support for the ocean theory. However, all telescopic detections reported were made at the limit of sensitivity of the data5,6,7, thereby calling for a search for plume signatures in in-situ measurements. Here, we report in-situ evidence of a plume on Europa from the magnetic field and plasma wave observations acquired on Galileo’s closest encounter with the moon. During this flyby, which dropped below 400 km altitude, the magnetometer8 recorded an approximately 1,000-kilometre-scale field rotation and a decrease of over 200 nT in field magnitude, and the Plasma Wave Spectrometer9 registered intense localized wave emissions indicative of a brief but substantial increase in plasma density. We show that the location, duration and variations of the magnetic field and plasma wave measurements are consistent with the interaction of Jupiter’s corotating plasma with Europa if a plume with characteristics inferred from Hubble images were erupting from the region of Europa’s thermal anomalies. These results provide strong independent evidence of the presence of plumes at Europa.

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Fig. 1: Galileo MAG data for the E12 flyby.
Fig. 2: Galileo plasma wave data and derived plasma density for the E12 flyby.
Fig. 3: Location of the modelled plume on Europa’s surface.


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We thank M. McGrath for an illuminating presentation at a Europa Clipper Project Science Group meeting on observations of Europa’s plumes, which led us to re-examine the Galileo MAG data on which this paper is largely based. The work at the University of Michigan was supported by NASA through grants #NNX12AM74G and #NNX15AH28G, contract #1532308 through the Jet Propulsion Laboratory and contract #143448 through the Applied Physics Laboratory at Johns Hopkins University. The research at the University of Iowa is supported by NASA through contract UTA16-001080 through the University of Texas at Austin. Additional funding for work at UCLA was provided by NASA grants #NNX13AL05G:000002 and #NNX14AO24G.

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X.J., M.G.K. and K.K.K. contributed to the analysis of the Galileo magnetic field data. W.S.K. analysed the Galileo plasma wave data. X.J. performed the simulations and led the interpretation of the model results. All authors discussed the results and contributed to writing the manuscript.

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Correspondence to Xianzhe Jia.

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Jia, X., Kivelson, M.G., Khurana, K.K. et al. Evidence of a plume on Europa from Galileo magnetic and plasma wave signatures. Nat Astron 2, 459–464 (2018).

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