• The ocean showed itself not with plumes or pools but via subtle changes in Ganymede’s aurora, the moon’s version of the Northern Lights.
  • Jupiter’s magnetic field should interfere with Ganymede’s, causing the moon’s aurora to rock back and forth by about 6 degrees. However observations showed that the aurora shifted by only about 2 degrees. The team deduced that an electrically conductive fluid beneath the surface — a saltwater ocean, for example — would create a secondary magnetic field that counteracted Jupiter’s interference.
  • Jupiter’s moon Europa and Saturn’s moon Enceladus also hide subsurface oceans and researchers suspect that there may be water within Jupiter’s moon Callisto and the dwarf planet Ceres.

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