Illustration of Galileo at Jupiter

The planet Jupiter, scientific objective of NASA's Galileo mission, scheduled for launch this week, has recently exhibited dramatic changes in major atmospheric feature.

Complementary observations made at the NASA Infrared Telescope Facility on Mauna Kea and at the Tortugas Mountain Observatory near Las Cruces, New Mexico, show that the South Equatorial Belt, dark feature circling Jupiter just north of the Great Red Spot, has faded out.

This change which appears to involve mid-level clouds, occurred over few months during the past summer. The corresponding North Equatorial Belt remains dark, and Jupiter's high cloud layer and stratosphere also appear unchanged.

The infrared observations were carried out by an International Jupiter Watch team organized by Dr. Glenn Orton, planetary scientist at the Jet Propulsion Laboratory (JPL) and member of Project Galileo's science team, with the cooperation of many scientists.

Concurrent observations in visible (blue-green) light and in the near-infrared band associated with atmospheric methane were made by Dr. Reta Beebe, Scott Murrell and David Kuehn of New Mexico State University in Las Cruces. They used the University's 24-inch telescope at Tortugas Mountain with JPL provided CCD sensor. Dr. Beebe is member of the Voyager imaging team.

The observations were part of NASA's Planetary Astronomy Program, which carries out Earth-based research to complement the spacecraft-based exploration of the solar system.

This brightening of normally dark belts has occurred at various Jovian latitudes at various times in the past, and many astronomers have observed it in visible light.

The South Equatorial Belt faded in the early l970s, when Pioneer l0 and ll flew by Jupiter, but turned dark again in l974 and remained so through both Voyager encounters and until April l989, according to Dr. Orton.

"This is the first time we have been able to correlate thermal infrared, methane-band and visible-light images of the change, and over so large region," he said.

The Galileo mission is designed to study Jupiter's atmosphere in many ways. Galileo's atmospheric probe will descend slowly through the cloud layers in December l995. The Galileo orbiter, after observing Jupiter for months as it approaches, will study the planet in many wavelengths from ultraviolet to infrared and radio bands during 1995-l997 orbital tour.

Project Galileo is managed by JPL for NASA's Office of Space Science and Applications, which also manages the Planetary Astronomy Program.

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