Io may generate a magnetic field of its own

17 Jun 2002

The Galileo spacecraft recently measured the magnetic field in the vicinity of Jupiter's moon Io and found the field strength to be approximately 38% lower than the 1860 nanotesla expected if only the field originating at Jupiter itself were present. Researchers have previously speculated that additional fields may be generated near Io by the presence of accelerating ions in the moon's neighborhood.

But at the May meeting of the American Geophysical Union in Baltimore, Margaret Kivelson of UCLA suggested that even the most charitable estimates on the numbers of ions encountered by Galileo during the measurements could not account for this sharp dip in the magnetic field. The most likely way to explain the results, Kivelson said, would be if Io's core (known to be heavy and currently believed to consist of iron or an iron-iron sulfide mixture) generates a magnetic field, perhaps through the sloshing of molten fluid, as speculated happens in the cores of Earth and Mercury. If this hypothesis holds up to more detailed analyses of Galileo's ion flux measurements, Io would be the first moon known to produce its own magnetic field, Kivelson noted in an article in Physics Today.