Galileo continues to orbit around Jupiter this week, traveling away from the heart of the system after
completing a close flyby of Jupiter’s icy moon Europa last week. The spacecraft spends the week
returning data acquired during its November flyby of Jupiter’s volcanic moon Io. The data are stored
on the spacecraft’s onboard tape recorder. Data playback is interrupted on Friday so the spacecraft
can perform regular maintenance on its propulsion systems.

During data playback, the spacecraft computer retrieves the stored data from the tape recorder,
then processes and packages the data, and subsequently transmits the data to Earth. Here on Earth,
the large antennas of the Deep Space Network capture Galileo’s radio transmissions and send them to
the Jet Propulsion Laboratory, in Pasadena, California, for ground processing, and, ultimately, delivery
to the science community. The large antennas of the Deep Space Network are located near Madrid,
Spain, Canberra, Australia, and Goldstone, California.

The data returned this week are taken from a 3-hour high resolution recording of the Io plasma torus
performed by Galileo’s suite of Fields and Particles instruments. The Fields and Particles instruments
are comprised of the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer,
Plasma Detector, and Plasma Wave instrument. The recording gathered data from 6 Jupiter radii
(429,000 kilometers or 267,000 miles) above Jupiter’s cloud tops down to an altitude of 5 Jupiter radii
(357,000 kilometers or 222,000 miles), making it the third deepest set of torus measurements of
Galileo’s entire mission to date.

The Io torus is a doughnut-shaped region of space with its inner edge bounded by Io’s orbit. It
contains intense plasma and radiation activity with strong magnetic and electric fields. The torus is
believed to be constantly supplied by volcanic activity on Io. The data acquired by the recording will be
used to understand the structure and dynamics of the plasma, dust, and electric and magnetic fields
present in the torus region. The data will also shed light on the overall dynamics of the Jovian

For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home
page at one of the following URL’s: