Galileo

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The first spacecraft designed to orbit the planet Jupiter and send a probe into its atmosphere, Galileo was launched on Oct. 18, 1989, from a Space Shuttle. Its path took it by Venus once and Earth twice for gravitational assists to reach its destination. The flight also included flybys of asteroids Gaspra and Ida and an encounter with a dense dust storm near Jupiter. In December 1995, Galileo passed the volcanic Galilean moon Io and entered Jovian orbit. Thereafter its flight, with further gravitational aids, has enabled it to view the other Galilean moons closely: Callisto, Europa, and Ganymede. The spacecraft's electric generator is powered by a plutonium isotope. Because its main communication antenna remains stuck, Galileo uses a slower backup link to relay data.Approximately 150 days before reaching Jovian orbit, Galileo separated from its probe, which was aimed toward one of the parallel belts considered representative of Jupiter's dense atmosphere. On Dec. 7, 1995, the probe recorded atmospheric data for 57 minutes, reaching a depth of more than 600 km (370 mi) before being crushed by pressures greater than 22 times that of Earth's atmosphere at sea level. Its instruments monitored lightning activity, thermal balance, the helium-hydrogen ratio, and the size of cloud particles. As it descended through unexpectedly clear and lightning-free skies the probe detected increasingly strong winds and intense turbulence, driven by heat escaping from the planet's interior. The levels of helium, neon, oxygen, some heavier elements, and water were lower than some theories of planetary formation had led scientists to anticipate.