WASHINGTON – After eight years surveying Jupiter and its moons, NASA is giving its pioneering Galileo spacecraft an unusual but fitting send-off by steering it on a suicide course for the giant gas planet whose mysteries it has unraveled.
The 2 1/2-ton probe will plunge into the thick Jovian atmosphere today at 12:49 p.m. PDT, disintegrating moments later from the friction generated by its 108,000-mph descent.
Scientists at the Jet Propulsion Laboratory, who have planned Galileo’s demise for more than two years, say the craft’s fuel tanks are nearly dry and its radiation-fried electronics are faltering. But they vow that Galileo would go down fighting. “We expect to be collecting science data all the way in,” says JPL project manager Claudia Alexander.
Galileo’s 35th and final orbit of Jupiter will be a victory lap for a spacecraft that gave its creators fits, then outdistanced their expectations. After near-crippling mechanical failures en route, the spacecraft rebounded to rewrite most of what scientists knew about the makeup of Jupiter and its moons.
Ironically, one of Galileo’s own discoveries sealed its fate: signs of briny oceans churning beneath the frozen crust of Europa and two other Jovian moons. Fearing that the fuel-starved craft might accidentally crash into one of them – possibly spreading stowaway germs that would undermine future searches for life – NASA decided to destroy Galileo rather than let it dodder around the cosmos, as it does with most retired probes.
For the 800 scientists and engineers who worked on the project from conception to crash, today is bittersweet. Many have gathered in Pasadena, Calif., home of the Jet Propulsion Laboratory, to watch the spacecraft’s final moments.
Looking back, some Galileo alumni marvel that the star-crossed, $1.5 billion spacecraft made it to Jupiter at all.
But 58 minutes was all it took for Galileo to erase years of doubt and worry.
Five months before its arrival, the spacecraft discharged a 750-pound wok-shaped atmospheric probe designed to parachute into Jupiter’s atmosphere and relay measurements back to Earth. It was the first earthly object to penetrate a gaseous planet’s harsh inner-realm.
The probe had no propulsion system, and to conserve energy it remained silent until it began its 106,000-mph plunge into the clouds. On Dec. 7, 1995, at 3:10 p.m. PDT, the probe signaled that it was on its way.
“When we knew the probe worked,” says Young, who headed the experiment, “there were tears in people’s eyes.”
Two hours later, after a 2.3 billion-mile trip, Galileo fired its main engine and entered orbit. The probe, meanwhile, had survived for 58 minutes and penetrated 125 miles through the clouds.
The measurements it radioed back have rewritten most of what scientists know about the composition of Jupiter’s atmosphere.
Scientists, for example, were startled to find that Jupiter contained more carbon, nitrogen and sulfur than the sun – even though both bodies were thought to have emerged from the same gaseous galactic birthing ground. “It’s caused a major rethinking of our theories of planetary formation,” Young says. “We still don’t see how Jupiter could have formed.”
Even more surprises emerged during Galileo’s survey of the four innermost and largest of Jupiter’s 61 known moons – Io, Ganymede, Callisto and particularly Europa.
“Europa is the star of the show,” says imaging team leader Michael Belton. Before Galileo, he says, the best photographs of Europa showed only an “icy fuzzball with fuzzy markings.”
But the spacecraft’s camera and instruments documented dramatic frozen ice domes and icebergs concealing what could be a vast, salty and possibly warm ocean. “What Galileo has done by proving that there is an ocean,” says Belton, “is basically transform it from a mere moon into a prime candidate as a habitat for extraterrestrial life.”
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