- Jupiter's aurora feels Europa's light touch

<< Several of Jupiter's moons are thought to play a role [of Jupiter's aurora]. In the case of Io, scientists believe the moon's ongoing volcanism produces gases which become charged and carry strong electrical currents along the arcing magnetic lines into Jupiter's atmosphere.

Something in the air?

"A very similar process apparently occurs at Europa," Grodent's team writes, having studied 45 Hubble images of the aurora showing the moon's footprint and tail. But Europa is not thought to be volcanic, so what could produce the electrical current that zips along and eventually gives rise to Europa's auroral footprint? >>

Sputtered ions from the surface?

" 'We're looking for something either within the moon's surface or in its atmosphere that's electrically conducting,' says John Clarke, a space physicist at Boston University, US. While the surface is a possibility, Clarke told New Scientist, the ionosphere should be the first place to look."

Well, thanks to its (near-certain) subsurface ocean, Europa's near-surface is very conductive indeed. While I know almost nothing about the physics of flux tubes, I think that in the case of Europa, the surface should actually be Suspect #1 -- the studies of Europa's induced magnetic field by Galileo long ago ruled out any ionosphere for it even remotely conductive enough to generate the kind of induced magnetic field that they were seeing near that moon.