Galileo Takes Close-Ups of Icy Europa
Two years after the Galileo spacecraft sent a probe plunging into giant Jupiter’s swirling pink and yellow clouds, the craft marked the end of its primary mission and the start of an extended mission by zooming in on the frozen Jovian moon Europa for the closest pass yet, snapping pictures from a mere 124 miles overhead early Tuesday.
Although those images are not yet available, pictures taken during a fly-by Nov. 6 revealed a heavily scarred surface pockmarked with blisters and scratched with long parallel ridges, as if a giant cat had clawed it. “Europa is really the gem of the solar system,” said Ron Greeley of Arizona State University.
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Scientists at the Jet Propulsion Laboratory announced Tuesday that the mission has been reborn as the GEM project, or Galileo Europa Mission. During the next two years, Galileo will swing by Europa eight times, swooping in for close looks at the chopped ice surface that may blanket the only extraterrestrial ocean in the solar system.
With its crust of ice and heart of metal and rock, the moon is one of the few sites in the solar system that might have harbored life. The big unknown, Greeley said, is “has that heart been warm in recent geologic history?” Only a warm Europa would have supported liquid water, a requirement for life.
Images already sent back to Earth by Galileo offer stark evidence that at some point in Europa’s history, the underlying slush was warm enough to rise and rip the ice-crusted surface apart. However, researchers don’t agree on how long ago that warm spell might have been, or how long it lasted. Estimates range from 3 million to 3 billion years ago, said Galileo project scientist Torrence Johnson.
During its extended mission, Galileo will look for clues that might help resolve the dispute, he said, although “really determining whether there is an ocean” beneath the ice today is beyond the scope of Galileo and will have to await future missions.
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The question of whether an ocean sloshes beneath Europa’s surface is of special interest to earthlings, themselves born of the salty sea.
NASA’s focus on finding signs of ancient life on other worlds has intensified since the tentative discovery of ancient fossil-like forms on a meteorite from Mars last summer.
Whatever Galileo comes up with during the next two years, the primary part of the mission already reaped enough new information to keep the researchers busy rewriting the textbooks on the Jupiter system, Johnson said.
Since Dec. 7, 1995, when the Galileo probe slid perfectly beneath the Jovian clouds and the mother ship began its two-year odyssey around the largest planet in the solar system, the mission has been surprisingly smooth. It marked the first descent into the atmosphere of any of the giant outer planets as well as the first orbital tour around an outer planet.
The successes were especially gratifying after the series of potentially devastating setbacks, including a launch delayed by several years, a main antenna that didn’t unfurl and a malfunctioning tape recorder.
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Without the main antenna, Galileo scientists have had to make do with meager dribbles of data compared to the flood they expected. Even so, the satellite has already sent down more than 1,800 images of the giant planet and its four major moons.
Outgoing project manager Bill O’Neil recalled “two glorious years” in which Galileo served as “our human presence on Jupiter. It is our eyes, ears, touch and taste.”
Among the things those eyes and ears saw and heard were thunderstorms hundreds of times more powerful than those on Earth, accompanied by flashes of lightning “appropriate for the god of thunder,” Johnson said.
Galileo saw lava flows on Jupiter’s violent moon Io the likes of which have not been seen on Earth for 3 billion years. It saw salts and floating ice rafts on Europa’s cracked surface, and discovered a magnetic field on the huge moon Ganymede.
Scientists were able to extend the mission, in part, because of the efficient way in which Galileo used the gravity boosts from Jupiter’s moons to propel itself around the miniature planetary system. Enough propellant was left over to keep the spacecraft operating at least through late 1999.
After its eight Europa fly-bys, Galileo will round the moon Callisto four times in order to brake and coast in toward the volcanic moon Io. Assuming the spacecraft’s electronics aren’t destroyed by Io’s fierce radiation, it will make two close passes by that moon.
Eventually, the electronic systems will fail, propellant will run out, and Galileo will continue to circle Jupiter as one of its retinue of 16 moons. There is a small chance--perhaps 1%--that it might crash into one of the moons or even get flung out of the Jupiter system altogether sometime within the next 50 years, researchers said.
