Fluke Gives Scientists Double Look at Jupiter

A spacecraft that was supposed to die a natural death in 1997 is now being joined near Jupiter by a newer craft, unexpectedly giving scientists the chance to “double team” the giant gas planet, officials at the Jet Propulsion Laboratory in Pasadena said Saturday.

Scientists gathering to mark the event at JPL released the first recordings ever made of the “bizarre sounds of Jupiter,” the first images of the mysterious magnetic bubble that surrounds the planet, and new images that show particles spewed from volcanoes on the moon Io stretching out from the planet for 13 million miles--and possibly reaching Earth.

At this point, the story is not so much about what the instruments have found, but about what the steady streams of data will have to say: They could explain the workings of the magnetic field around Jupiter, the planet’s faint Saturn-like rings and its turbulent thunderstorms --the size of Earth--that persist for centuries.

It is also the Cinderella story of an aging, creaky spacecraft, Galileo, that returned inexplicably for a last day in the sun.

“For it to have survived 2 1/2 times as long as its mission length in a hazardous environment, Galileo is very much the hero here,” said Robert T. Mitchell, who manages the newer Cassini mission for NASA’s JPL. Engineers have taken to calling Galileo “the little spacecraft that could.”

The jubilant and unexpected success of Galileo is a much needed boost for JPL, which suffered the loss of two high-profile missions to Mars last year and is under pressure to improve its track record.

“The question of the year is why [Galileo has] been able to survive three times the radiation it was supposed to,” said Jim Erickson, who manages the mission and the team of engineers who keep the craft healthy with software reboots and occasional round-the-clock baby-sitting.

In addition to planetary science, the geriatric craft is spawning a slew of papers about the longevity of space-borne electronics, he said.

If all had gone according to plan, there would be only one spacecraft near Jupiter now--the $3.26-billion Cassini, a 22-foot, 12,000-pound behemoth launched in the fall of 1997. It has just reached Jupiter and will use the planet’s massive gravitational field to slingshot itself to its final destination, Saturn.

But Cassini’s predecessor, Galileo, decided not to play by the rules. When Galileo kept working eight years after its 1989 launch, NASA officials extended its mission until January 2000--but thought it would surely then be poisoned by Jupiter’s notorious radiation belts.

Though aging, creaky and sprinkled with failed semiconductors, the 5,000-pound instrument keeps going and going, an Energizer bunny of a spacecraft. Galileo’s longevity is the only reason scientists now have their first double bird’s-eye view of the giant gas planet. They say that has happened previously with only one other planet: Earth.

Saturday, Cassini was about 6 million miles from Jupiter, while Galileo was about 300,000 miles from the surface, well within the planet’s huge magnetic field. Scientists have long believed that the magnetic field surrounding Jupiter like an invisible bubble is strongly influenced by the solar wind--streams of energized particles flowing from the sun and buffeting everything, including planets, that stand in their way.

By using two spacecraft, scientists can now test that idea. Cassini can measure changes in the solar wind as Galileo simultaneously monitors the planet’s magnetic field, or magnetosphere. Until now, “we’ve had no weather station upstream in the solar wind to tell us how the magnetosphere might be responding,” said William Kurth, a planetary scientist at the University of Iowa who is running instruments on both spacecraft.

Kurth and a team of Cassini and Galileo scientists presented their results Saturday morning at JPL, just hours after Cassini had reached a milestone, coming the closest it would to Jupiter while on its 3.5-billion-mile journey to Saturn.

At the briefing, Kurth presented the actual “sounds of Jupiter,” playing a bubbling, screeching tape of noises recorded by Cassini as it passed through disturbances caused by energetic particles that make up the planet’s magnetosphere. Though they represent something like a sonic boom on Earth, the noises sounded like a troop of howler monkeys battling underwater. “We’ve all got our impressions of what these noises sound like,” Kurth quipped.

Meanwhile, another instrument has revealed for the first time the structure of the magnetosphere--and shown that it is not uniform, but is a hodgepodge of “lumps, tails and threads,” said Stamatios “Tom” Krimigis, who heads the space department of the Johns Hopkins University Applied Physics Laboratory. Krimigis is also lead investigator on the instrument that is imaging the magnetosphere by capturing atoms that occasionally escape from it.

The magnetosphere of Jupiter is now twice as large as it was in 1979, when Voyager examined the planet, and has no doubt expanded and shrunk repeatedly in that time, said Krimigis, who was also a lead scientist on the early mission. In another experiment, Krimigis found that particles spewed from the volcanoes of Io are spun out 13 million miles from the surface of Jupiter, forming a huge nebula around the planet.

Carolyn Porco, an expert on planetary rings who leads Cassini’s imaging science team, released images of Jupiter that are startlingly sharp for photos taken from 6 million miles away. “It’s performed beyond our wildest imagining,” she said. “These photos are like my babies. I’ve been waiting 10 years for them.”

The photos clearly show particles and tiny moons within the swirling rings. Porco is hoping to determine if the rings are largely made of rocky particles, rather than ice like Saturn’s rings, and whether those particles originate from the moons within the rings.

Other images show Jupiter’s well-known Red Spot--a 300-year-old storm much larger than the entire surface of Earth--and the bands of long-lived atmospheric turbulence that cross the planet. Although Cassini is farther from Jupiter than Galileo is, it has a better camera and is able to take time-lapse photos of the planet. From these, Porco’s team created a movie of the streaming bands of Jupiter’s turbulent atmosphere and storms swirling past the more stable Red Spot.

“I don’t know about you, but I can get lost looking at this,” she said of the abstract images.

Analysis of the movies shows huge storms forming, merging and being sheared apart in the tortured Jovian atmosphere. Further analysis, said Andrew Ingersoll, an expert on planetary weather at Caltech, could answer the long-standing question of where the turbulent atmosphere obtains the energy that is pushing it.

Are the smaller storms “parasites that are deriving their energy from the big guys like the Red Spot?” Or are “the little guys the primary harvesters of energy and the big guys eat them?” he asked.

“Stay tuned, folks,” he said. “There’s lots more to come.” Jupiter might even shed light on our planet’s tamer, but more capricious, weather. “We’d like to understand why the Earth’s weather is so transient, while Jupiter’s is so long-lived,” he said.

Meanwhile, what is to happen to trusty Galileo? There are no plans for a funeral yet. The spacecraft is scheduled to fly by Jupiter’s moon Callisto in May and then pass near Io several times later in 2001.

For the new images and sounds from Jupiter, go to: https://www.jpl.nasa.gov/