Galileo Turns Attention to Jupiter, Jupiter's Rings and Io

The focus of Galileo's encounter turns away from Ganymede and Europa today, and toward observations of Jupiter, Jupiter's rings and Io. Observing activities are interrupted once today while the spacecraft performs a standard gyroscope performance test and a test to slew its scan platform.

The Photopolarimeter Radiometer (PPR) is first to observe this morning, taking data for a thermal map of the recently-merged white ovals in Jupiter's atmosphere. White ovals are storms that occur between two adjacent zonal jet streams, and have lasted for decades. However, two of them have merged within the past few months to create a single storm. Next, PPR performs two scans of Jupiter's limb. These observations are designed to detect upwellings in Jupiter's atmosphere. The Near-Infrared Mapping Spectrometer (NIMS) continues observation of Jupiter with a spectral scan of its North Equatorial Belt. The NIMS observation is performed in realtime, which means that the data are not stored on the spacecraft's tape recorder, but rather are directly transmitted to Earth after processing and packaging.

The Plasma Wave instrument (PWS) performs the next observation in conjunction with instruments on the Cassini spacecraft. The Cassini spacecraft is approaching Jupiter enroute to arrival at Saturn in 2004. Cassini will pass closest to Jupiter in December 2000, where it will perform more coordinated observations with Galileo. The current joint observation is designed to study the properties of radio-frequency emissions from Jupiter.

NIMS returns to observing Jupiter's atmosphere with a spectral scan of the North Temperate Zone. This observation is again performed in realtime. PPR is next to observe, but this time the target is Io. In a pair of observations taken at different solar phase angles, PPR will obtain data on the texture and small-scale properties of Io's surface. The Solid-State Imaging camera (SSI) shifts attention to another target by capturing a few images of Jupiter's rings. The images will be taken at relatively high resolution, low solar phase angle, and high tilt angle. They will provide scientists with better determinations of the size and distribution of ring particles, both within Jupiter's main ring, and at its inner edge. The images will also attempt to detect wavelike features in the main ring and undulations in the ring's outer boundary, which would be important for understanding how the rings are maintained by the small inner satellites.

NIMS wraps up the observing day with six more observations. The first four are realtime scans of Jupiter's North Equatorial Belt and North Temperate Zone. For the last two observations, NIMS performs spectral scans of Jupiter's bright limb. The scans will be used to provide scientists with data on the equatorial bulge created by Jupiter's rotation.

Think the fun is over? Think again! Come back tomorrow for more observations of Jupiter's atmosphere.