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Scientists Begin to Decipher Surprising Jupiter Probe Data

By K.C. Cole
Los Angeles Times

Prying open a cosmic tomb that has been tightly sealed for 4.6 billion years, the Jupiter probe Galileo has revealed puzzles and surprises that promise 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 last December. About half of the expected helium is missing, as well 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 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 many 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. Earth can trace its ancestry back to the original swirl of gases that formed Jupiter.

The data shows that astronomers 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," said Johnson.

Gathered Monday at NASA Ames Research Center in Mountain View, Calif., the scientists 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 Santa Clara University. 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 resulted from unusually calm weather at the spot where the probe entered the atmosphere.

Based on previous observations of Jupiter from Earth and from Voyager spacecraft, researchers had expected to find significant quantities of carbon, sulfur, nitrogen and oxygen. They had assumed that Jupiter got these heavier elements from the same source as Earth's - notably, bombardment by icy comets during the early, more violent, years of the solar system.

But instead they found only traces of these 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 Ames Research Center.

The finding that Jupiter seems to be almost entirely made of hydrogen and helium means it's surprisingly like the sun.

Until now, scientists entertained two conflicting views of how Jupiter became the biggest planet in the solar system: One scenario had it forming like a partner to the sun - a star that never ignited.

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 toward the failed star scenario. They also make scientists wonder about the composition of Jupiter's sister planets, Uranus and Neptune, which were also studied from Voyager and Earth observations.

"This is really strange," said Kevin Baines of Jet Propulsion Laboratory in Pasadena, Calif., who studies the outer giant planets. 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 biggest surprise of the latest mission was that Jupiter's high winds do not taper off, even at a hundred miles below its ammonia clouds, said Morrison.

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," said Morrison. Another major revision is likely to come from finding about half the expected amount of helium.Researchers speculated that it might be raining into the planet's core (along with neon, which also failed to make its expected appearance).