DALLAS -- The Galileo spacecraft just keeps going and going, despite a crippled antenna.
Two years after the probe started exploring Jupiter and its moons, NASA has decided to extend the Galileo mission for another 24 months.
"We've got a healthy spacecraft and funding for the next two years," said Bob Mitchell, Galileo project manager at the Jet Propulsion Laboratory in Pasadena, Calif. "We could hardly have hoped for as much two years ago."
Galileo's main antenna never opened properly after its 1989 launch. Still, once it arrived at Jupiter in 1995, the probe managed to relay more than 1,800 stunning images through its backup antenna. Scientists have learned about violent thunderstorms on Jupiter, huge volcanic eruptions on its moon Io, and much more.
With Galileo's new lease on life, researchers hope to concentrate on Jupiter's most intriguing moon, Europa.
The latest images from Galileo support the idea that Europa's icy surface hides a layer of warm slush or even water. That would make it the only place in the solar system, other than Earth, known to contain life-sustaining liquid water.
"Europa really is the gem of the solar system," said Arizona State University geologist Ronald Greeley at a news conference last week.
The extension of the mission calls for Galileo to swoop by Europa eight times within 14 months. The first and best of these close encounters came Tuesday, when the spacecraft flew 124 miles lTC above Europa's surface.
Scientists won't get pictures back from that encounter for a few more weeks. But in the meantime, they're busy looking at the latest Europa images, snapped during a flyby Nov. 6. Those pictures show areas never seen before, covered with features that support the notion of a buried ocean.
Structures that look like giant blisters may have formed as warm material welled up from inside Europa like giant blobs within a lava lamp, Greeley said. Heat inside Europa, from radioactive minerals and from the friction of being tugged around by Jupiter's gravitational pull, might keep Europa warm enough that its interior is molten.
Other recent pictures show how the lava-lamp blobs may have carried minerals toward the surface. Instruments aboard Galileo have found areas where magnesium and sulfate-rich salts are concentrated, possibly having been carried there in the blobs.
Such evidence suggests that Europa was once partly liquid. "But the big unknown is the timing of events," said Greeley. "Has Europa's heart been warm throughout geological history?"
Some researchers believe Europa has been geologically active during the past several million years; others think it's been quiet for at least 3 billion years, Greeley said. Galileo might be able to pin down the answer during its extended mission by taking pictures of new areas of Europa, he added.
If Galileo makes it through the next two years, it could also tell scientists about more than just Europa. After the eight Europa encounters, mission controllers plan to fly the spacecraft past Jupiter's moon Callisto four times. This path will nudge the probe through the Io torus, a giant doughnut of charged particles that surrounds Io. Scientists want to learn as much about the torus as they can, including what creates it and what effect it has on the moons, said Karen Buxbaum, Galileo's science planning manager at the Jet Propulsion Laboratory.
By late 1999, Galileo should have reached its final target: two close flybys of Io to study and photograph its volcanic activity.
After that, the probe will probably run out of fuel and succumb to the harsh radiation that surrounds Io. Eventually Galileo will end up circling Jupiter as a piece of space junk, said Mitchell, the project manager.
The extended Galileo mission will cost $30 million, a relative bargain compared with the probe's main budget of $1.3 billion.
No matter what scientists find in the next two years with Galileo, they're pleased by what the probe has already discovered.
In addition to the Europa findings, mission highlights include: Discovering spectacular thunderstorms on Jupiter, with lightning bolts 10 to 100 times more powerful than those on Earth;
Detecting a magnetic field, stronger than Mercury's, around Jupiter's largest moon, Ganymede;
Learning that Europa, Io and Ganymede all have metallic cores, while Callisto, oddly, does not;
Observing volcanic eruptions on Io, including one that covered an area the size of Arizona in four months.
Even if the spacecraft were to die tomorrow, Galileo has already sent back "fabulous" results, said chief scientist Torrence Johnson of the Pasadena lab.
Pub Date: 12/22/97