Ultraviolet emissions from the magnetic footprints of Io, Ganymede and Europa on Jupiter


Io leaves a magnetic footprint on Jupiter's upper atmosphere that appears as a spot of ultraviolet emission that remains fixed underneath Io as Jupiter rotates1,2,3. The specific physical mechanisms responsible for generating those emissions are not well understood, but in general the spot seems to arise because of an electromagnetic interaction between Jupiter's magnetic field and the plasma surrounding Io, driving currents of around 1 million amperes down through Jupiter's ionosphere4,5,6. The other galilean satellites may also leave footprints, and the presence or absence of such footprints should illuminate the underlying physical mechanism by revealing the strengths of the currents linking the satellites to Jupiter. Here we report persistent, faint, far-ultraviolet emission from the jovian footprints of Ganymede and Europa. We also show that Io's magnetic footprint extends well beyond the immediate vicinity of Io's flux-tube interaction with Jupiter, and much farther than predicted theoretically4,5,6; the emission persists for several hours downstream. We infer from these data that Ganymede and Europa have persistent interactions with Jupiter's magnetic field despite their thin atmospheres.

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Figure 1: Composite of images with the STIS UV-MAMA (multi-anode microchannel array) of Jupiter's north and south polar regions.
Figure 2: Polar views of north and south auroral zones on Jupiter, showing the observed locations of ultraviolet emissions.
Figure 3: Brightness traces across the ultraviolet footprint emissions of Io in the direction corresponding to the plasma flow, or approximately east–west on Jupiter.


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This work is based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA for NASA. The research was supported by grants from the Space Telescope Science Institute and from NASA to the University of Michigan. J.T.C. acknowledges the hospitality of the Institut d'Astrophysique du CNRS in Paris during the preparation of this paper, and J.C.G. and D.G. acknowledge support from the Belgian Fund for Scientific Research and the PRODEX program of ESA. L.B.J. acknowledges support from the Institut National des Sciences de l'Univers and the PNP programme.

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Correspondence to J. T. Clarke.

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Clarke, J., Ajello, J., Ballester, G. et al. Ultraviolet emissions from the magnetic footprints of Io, Ganymede and Europa on Jupiter. Nature 415, 997–1000 (2002). https://doi.org/10.1038/415997a

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