Revised Galileo Results Pose Jovian Puzzle

Article excerpt

Some 4.5 billion years ago, a sizable fraction of the gas and dust that cloaked the infant sun assembled into a solid core 10 times as massive as Earth. This solid body then grabbed nearly 30 times its weight in hydrogen and helium from the solar nebula, forming the biggest planet in the solar system. On that, planetary scientists generally agree. But a new analysis of data gathered by the Galileo probe, which parachuted into Jupiter last December (SN: 12/23&30/95, p. 420), has thrown detailed theories ab out the giant planet's origin into disarray.

Jupiter's atmosphere-at least the region explored by the Galileo probe-appears unusually dry, containing only one-fifth the abundance of water scientists had predicted. They used as a benchmark the sun's oxygen-to-hydrogen ratio because Jupiter originated from material that swaddled the sun. Donald M. Hunten of the University of Arizona in Tucson reported the latest analysis last week at the annual Lunar and Planetary Science Conference in Houston.

The new report contains the second revision of the scientists' estimate of Jupiter's water supply, which they derive from data recorded by the probe's mass spectrometer. The current value, announced after researchers carefully calibrated a duplicate of th e spectrometer sent to Jupiter, is nearly the same as the original value reported by Science News last December and one-fifth that calculated in January (SN: 1/27/96, p. 55).

Other detectors on the probe also found evidence of a dry Jupiter. The absence of water clouds, the relative rarity of lightning, and the infrared emission that water would have blocked all suggest that the probe encountered little water vapor. "It's over whelming," declared atmospheric scientist Andrew P. Ingersoll of the California Institute of Technology in Pasadena at the conference.

The finding, he adds, leaves open three possibilities, none of which seems appealing. …