While on its journey to Saturn, the Cassini spacecraft makes its closest approach to Jupiter. The flyby provides Cassini with a gravitational boost for reaching Saturn and also provides the first chance to study a gas giant planet with two nearby spacecraft simultaneously. NASA's Galileo spacecraft, orbiting Jupiter since 1995 and still functioning beyond its originally planned two-year mission, teams with Cassini to study the planet.

The collaborative study provides new insight into how the solar wind of particles speeding away from the Sun affects a huge magnetic region, the magnetosphere, encasing Jupiter. While Cassini monitors the solar wind just upstream, Galileo watches for changes inside the magnetosphere. Scientists learn the magnetosphere is lopsided and leaky, with an unexpected abundance of high-energy particles bleeding out from one side

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