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Galileo flies past Amalthea in the final science mission of an extraordinary eight-year reconnaissance of the jovian system.
As alien clouds billow up from chasms of swirling fog, a star streaks across the purple sky, trailing sparks and incandescent debris in its wake. This is the end of Galileo, an ambitious and incredibly successful mission of discovery. Since 1995, the Galileo spacecraft has orbited Jupiter, charting its moons, sampling its magnetic field, and weathering a constant storm of radiation. Even in its last loop around Jupiter, the craft continued to be remarkably productive, with a scientifically surprising flyby of the inner moon Amalthea. The dramatic conclusion to its illustrious mission, slated for September 21, 2003, will culminate with a suicide dive into the jovian clouds.
At its launch in 1989, no one anticipated such an end. Long before the 3-ton explorer first swooped past Jupiter's innermost large moon, Io, mission planners knew they faced trouble. A main antenna that never unfurled properly sent flight engineers scrambling to get a fire hose of science data through a soda straw of the tiny, omni-directional antenna designed for low data rates. But the plucky Galileo, battered by micrometeorites, seared by deadly radiation, and hamstrung by its folded antenna, just wouldn't die. Living years beyond its design life, the craft flew extended missions to further explore Jupiter's most intriguing moons: Io and Europa. In all, Galileo completed 38 flybys of various planets (Earth twice and Venus once), asteroids (Gaspra and Ida), and Jupiter's four large moons.
The data Galileo collected have yielded tantalizing hints of a global ocean hidden beneath the frozen surface of Europa. Due to the possibility - no matter how remote - that life might have gained a foothold in the suspected subsurface ocean, mission planners decided to target the craft for a destructive plunge into Jupiter. This avoids even the slim chance of a contaminating impact with the icy moon.
Galileo's discovery of Europa's global sea was one of many hard-won revelations of its long mission. "From the beginning, we had to overcome challenges," says Galileo Project Manager Eilene Theilig. "One of the greatest challenges was that we had to use a tiny omni-directional antenna [instead of the umbrella-like high-gain antenna], and we were...