ONE of Jupiter鈥檚 moons is broadcasting radio waves, say scientists who
have been analysing data from the Galileo spacecraft.
When Galileo flew past Ganymede last year, it made the unexpected discovery
that the moon has a magnetic field. The scientists suspected that it might act
like a giant radio transmitter, just as planets with magnetic fields do. These
fields can trap high-energy charged particles that emit
radiation鈥攊ncluding radio frequencies.
Early observations from the spacecraft picked up faint radio waves, but it
was unclear where they were coming from. 鈥淚t鈥檚 like listening for a very distant
radio station through a much closer local one,鈥� says William Kurth of the
University of Iowa. In Geophysical Research Letters (vol 24, p 2167), Kurth and
his colleagues report that they have now analysed data from two Galileo flybys,
in June and September 1996, to pinpoint the radio source more clearly. 鈥淲e鈥檙e
now 100 per cent sure that it鈥檚 coming from Ganymede,鈥� says team member Donald
Gurnett.
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