Jupiter Probe Finds Some Major Surprises
Prying open a cosmic tomb that has been tightly sealed for 4.6 billion years, the Jupiter probe Galileo has discovered a plethora of puzzles and surprises that promises to alter scientists’ thinking about the giant gas planet, and perhaps even the evolution of the solar system.
Jupiter is a lot drier, hotter, darker and more turbulent than previously thought, scientists announced Monday as they released the first data from Galileo, which plunged into Jupiter’s clouds in December. About half of the expected helium is missing, as well as some of the predicted methane, oxygen and sulfur. And its 330-mph jet streams appear to reach deeper into the belly of the planet than expected.
Acknowledging that these early findings are still quite tentative, Galileo project scientist Torrence Johnson said the new data didn’t fit what researchers expected to see. “It’s sort of like Cinderella’s stepsisters” trying to fit their big feet into a dainty glass slipper, he said. “It’s darned uncomfortable. The shoe pinches.”
Since scientists believe that Jupiter remains a pristine blob of the original cloud that formed the solar system, the probe findings are like an archeological discovery about our past. Every person, place and thing on Earth can trace its ancestry back to the original swirl of gases that formed Jupiter.
Not surprisingly to the researchers, the data shows that scientists know less than they thought they did about the birth and evolution of planets. “There’s always a sense of humility when the data comes in,” Johnson said.
The scientists gathered Monday at NASA Ames Research Center in Mountain View, Calif., had been waiting almost 20 years for this first-ever look at the gaseous insides of the planet.
The probe had a “very rough ride down” Dec. 7, said planetary meteorologist Al Feiff from the University of Santa Clara. The extreme turbulence, he said, “would have made for a very uncomfortable airplane ride.”
Nevertheless, all of the instruments on board performed “remarkably well,” said Galileo project manager William O’Neill, who called it a “marvelously successful mission.”
It’s possible that some of the surprising readings were due to unusually calm weather at the spot where the probe entered the atmosphere. Contrary to expectations, the probe did not see three distinct cloud layers, but only a “light fog” and a lot of wispy material below, said Boris Ragent, also of the University of Santa Clara. But the expected layer-cake structure was noticeably absent.
Based on previous observations of Jupiter from Earth and from Voyager spacecraft, researchers also had expected to find significant quantities of carbon, sulfur, nitrogen and oxygen. They have assumed that Jupiter got these heavier elements from the same source as Earth--notably, bombardment by icy comets during the early, more violent years of the solar system.
Instead they found only traces of those gases, a finding that could influence the way in which scientists think about the evolution of Earth and other planets. “I don’t think anybody fully understands the implications,” said David Morrison, head of space science at NASA’s Ames Research Center.
Perhaps both Jupiter and Earth scooped up less material from passing comets than previously thought. Or perhaps the elements are buried on Jupiter but too diluted in the vast ocean of hydrogen and helium to distinguish.
“I think it’s going to take a while to sort that out,” Morrison said.
The finding that Jupiter seems to be almost entirely hydrogen and helium means that it is surprisingly like the sun.
Until now, scientists entertained two conflicting views of how Jupiter got to be the biggest planet in the solar system: One scenario had it forming like a partner to the sun--a star that never got quite big enough to ignite.
The other scenario had it starting out with a rocky core about the size of Earth, then sucking in surrounding gas by sheer force of its enormous gravity.
The new findings seem to tilt opinion back toward the failed-star scenario. They also make scientists wonder about the composition of Jupiter’s sister planets, Uranus and Neptune, which also were studied from Voyager and Earth observations.
“This is really strange,” said Kevin Baines of the Jet Propulsion Laboratory, who studies the outer giants. Perhaps Voyager was wrong, he suggested, or the probe was wrong. Or perhaps both were right, and the probe happened to descend into an anomalous place where “some very strange chemistry [was] going on,” he said.
The lack of much water in the probe results was a particular disappointment to Caltech planetary scientist Andy Ingersoll, who bet colleagues that Jupiter would be at least five times wetter than the sun--and possibly even 10 times wetter.
Ingersoll based his calculation on the way the ripples spread out in the Jovian atmosphere after 1994’s crash landing of the comet Shoemaker-Levy. Even the Voyager missions estimated that Jupiter contained twice as much water as the sun. The Galileo probe, however, suggests that Jupiter is actually quite dry. That also means that Jupiter lacks oxygen--since it would be the oxygen that would combine with hydrogen to make H2O (water).
But according to Morrison, the biggest surprise of all was that Jupiter’s high winds do not taper off, even at a hundred miles below its ammonia clouds.
On Earth, the energy that drives the winds comes streaming in from the sun. Jupiter’s weather, however, appears to be inside out--with heat energy rising from the core and setting up strong convection currents.
“That’s a major change in our thinking about the weather on Jupiter,” Morrison said. Another major revision is likely to come from the finding that half the expected helium was missing. Researchers speculated that it might be raining into the planet’s core (along with neon, which also failed to make its expected appearance).
The probe’s results did not offer much insight into several other outstanding Jovian puzzles. For example, Voyager detected fierce lightning in very narrow bands at high latitudes. The Galileo probe found widely scattered lightning that seemed to be coming from many different sources. Although their instruments detected 50,000 lightning-like events, that amounted to only a third to a tenth of those on a typical day on Earth.
“We have a new set of data that doesn’t all fit into our preconceived notions,” Lou Lanzerotti of Bell Labs said. It’s even possible that the lightning on Jupiter is caused by some exotic mechanics unknown on Earth.
Ragent pointed out that lightning on Jupiter has cultural as well as scientific significance, since the god Jupiter is always depicted grasping lightning bolts in his hand and hurling them toward naughty mortals on Earth. “There are lightning bolts, but not as many as we thought.”
The biggest mystery of all may well be Jupiter’s pink and yellow colors, and on that issue, the probe was silent. Scientists had hoped to learn something about which chemical concoctions are responsible for the planet’s pastel palette.
However, “it’s still an open issue,” Morrison said. “Colors have always been one of the mysteries on Jupiter, and I think they’re going to remain a mystery.”
The panel of scientists at Ames made it clear that it would take at least a year of more research before they fully understand the results. After all, this was the first time ever that a probe had gotten the inside story on a giant gas planet.
And the going’s been especially slow since the data bits are drizzling down to Earth at a painfully sluggish pace. Since the loss of Galileo’s primary antenna, researchers have had to make do with a tiny secondary antenna that transmits information not much faster than a skilled 19th-century telegrapher using only dots and dashes.
The probe’s data comes in the form of digital bits. Close-up pictures of Jupiter will come from the orbiting Galileo mother ship, but will not arrive on Earth until July.
The mother ship is cruising at almost its farthest point from the planet, getting ready to swing around for a second look.
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Jupiter Findings
Contrary to expectations, weather on Jupiter appears to be hot, dry, clear, turbulent and windy with widely scattered lightning. Here are some of the findings that contradicted scientists’ expectations:
* Atmosphere: Oxygen, carbon and nitrogen are scarce, and helium shows up in only half the expected amount.
* Weather: Gusts of more than 330 mph blow 100 miles below the surface. Yet the layer-cake clouds that researchers had expected were conspicuously absent.
* Water: Only one-tenth the expected water was found, and no water clouds. It is possible, researchers say, that the probe slipped through an unusually clear hole in Jupiter’s clouds.
