The Legacy of Galileo - Keck Institute for Space Studies - Caltech

Challenging the Paradigm: The Legacy of Galileo
One of Voyager’s important results in 1979 was the discovery of Jupiter’s extremely tenuous
ring system, so different from Saturn’s bright, magnificent rings. Galileo observations were
able to identify the origin of the rings at Jupiter. Images taken with the rings back-lit by the
sun showed that the rings are associated with the tiny satellites, also discovered by Voyager,
with the vertical extent of each ring segment matching the range of inclination of the orbit of
its associated satellite (Figure 8). The rings are formed from dust particles ejected from the
satellites’ surfaces by micrometeoroid impacts, which then drift inward toward Jupiter under
the influence of gravitational, radiation and electromagnetic forces to produce the diffuse
ring bands seen in the images.
Figure 8: Rings associated with satellites.
Fiery Io was a high priority target for Galileo investigators. The intensity of radiation in
Jupiter’s magnetosphere is much higher at Io’s distance from Jupiter than at the more distant
moons, and engineering considerations severely limited close flyby of Io early in the mission.
However, even distant observations showed the volcanic activity discovered by Voyager was
continuing unabated. In the extended mission phase, Galileo’s better than expected
resistance to radiation damage permitted a series of close flyby to complement the more
distant monitoring. These observations allowed a detailed characterization of Io’s activity and
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