"An electrically conductive magma ocean should suppress the changes [that cause auroras] but they are observed to be present and strong," Roth said.
Volcanoes on Io
One of the four largest Galilean satellites of Jupiter, Io is covered with 150 known volcanic hotspots. Enormous plumes of dust and gas explode from the surface, stretching into space.
While the new results suggest that a global magma ocean doesn't seem to lie beneath the moon's crust, that magma could still lie in scattered pockets, Roth said. Rock melted by heat inside Io, generated by the tidal pull of Jupiter, could power the volcanoes, Roth noted.
Based on the new research, Io's molten iron core may be larger than scientists previously estimated. According to Roth, gravity measurements place the core anywhere from 37 to 52 percent of the moon's radius, while the new results estimate it at between 38 and 68 percent. He said that a core spanning 40 to 50 percent of the radius — nearly half the size of the moon — would work well with all current theories and measurements.