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Galileo released its entry probe July 13, 1995. The probe entered Jupiter's atmosphere December 7, 2005. It returned 58 minutes of data, during which time it parachuted through more than 150 kilometers (about 95 miles) of atmosphere and measured winds of about 725 kilometers per hour (about 450 miles per hour). It was finally crushed when atmospheric pressure exceeded 22 times that found at the Earth's surface.
The Galileo spacecraft went into orbit around Jupiter in December 1995. Its primary mission was two years long, but the spacecraft remained operational, and NASA extended its mission repeatedly. The first mission extension was primarily to study the icy moon Europa. Eight additional flybys of Europa revealed that it had a deep liquid water ocean under its planetary ice sheet. This raised hopes that life might eventually be found under the ice.
At the end of the Europa mission extension, Galileo made two close flybys of the moon Io to study its extensive volcanism. This brought the spacecraft deep into Jupiter's intense radiation fields. Because there was a significant probability that the radiation would damage or destroy the spacecraft, Io observations had been delayed until the other mission objectives had been achieved. In both flybys, radiation damage knocked Galileo off-line shortly before the close encounter, and JPL engineers labored to restart the craft's computer before losing all the potential data. But they were rewarded with spectacular images.
By September 2003, Galileo was nearly out of propellant. Due to the complex gravitational pulls produced by all of Jupiter's moons, without propellant the spacecraft would not stay in a stable orbit. There was some risk that it could eventually crash into one of the larger moons, including Europa. Since Galileo was powered by radiothermal isotope generators, and because it had not been sterilized to prevent biological contamination of the moons ‹no one had expected to find liquid water that far from the sun) this meant there was a small risk of contaminating Europa. So NASA and JPL agreed to destroy the spacecraft by directing it into Jupiter's dense atmosphere, where it would be vaporized. Galileo's flight team at JPL gave the old spacecraft its orders, and on September 21, 2003, it entered Jupiter's atmosphere and was destroyed. |
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