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Jupiter Provides A Number Of Surprises For Researchers

Tue., Jan. 23, 1996

The Galileo probe that plunged into the turbulent atmosphere of Jupiter last month has intensified one of the giant planet’s persistent mysteries: Where is the water?

Preliminary data released Monday reveal a Jovian atmosphere much drier than expected - in fact, with no more water content than the sun, scientists said in the first briefing on the probe’s findings since its arrival at Jupiter on Dec. 7.

There had been indications of water abundances ranging from two to 10 times that of the sun, based on decades-old data from the Voyager spacecraft and analysis of the impacts of a fragmented comet on Jupiter in 1994.

This and several other surprises in the Galileo results have launched arguments and a lively reassessment of theories on how Jupiter and the other planets formed and evolved out of the disk of dust and debris whirling around the sun.

For example, researchers said, the apparent low abundance of water on Jupiter indicates that collisions with smaller water-bearing bodies, such as comets, may not have played the significant role suggested by some in the early development of the planets - including the transport of water for Earth’s oceans.

The Galileo probe performed well despite the enormous stresses it experienced during its 373-mile descent before it was destroyed as predicted by extreme heat and pressure, according to probe manager Marcie Smith of the National Aeronautics and Space Administration’s Ames Research Center in Mountain View, Calif.

In addition to the unexpected dryness of the Jovian atmosphere, other surprises were discussed Monday by more than a dozen researchers in a televised briefing from Ames, which had been scheduled last month but was delayed by the federal government shutdown:

Lightning was detected by probe instruments at a rate only about one-tenth as frequent as on Earth - a “veritable absence of lightning,” according to one scientist - reducing the probability of finding complex organic molecules formed by electrical energy in the Jovian atmosphere. (The lightning probably is associated with the amount of water, scientists said, because lightning bolts detected earlier by the Voyager craft were located at the same altitude that water clouds were, in theory, presumed to have formed.)

The probe did not detect the three layers of clouds that most researchers had predicted based on a combination of theory, observation and computer models.

Instead of the anticipated 220-mph gales blowing in the probe’s entry zone, prevailing winds of up to 330 mph remained fairly constant as the probe descended, suggesting that the winds are driven by heat radiating upward through a mechanism resembling the Earth’s jet stream.

The amount of helium measured was about one-half what had been expected. Researchers said they believe both helium and neon are “raining out” of the upper atmosphere to become concentrated nearer the core.

The probe discovered an intense radiation belt about 31,000 miles above Jupiter’s cloud tops.

Traveling at entry speeds of more than 106,000 mph, the probe and its six instruments experienced braking forces of up to 230 times Earth’s gravity and temperatures twice those on the surface of the sun.

Tags: research

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