Today on Galileo
August 14-22, 1999
Back here on Earth, flight team members are in the process of analyzing engineering data to determine the cause of four spacecraft anomalies seen during the encounter. Preliminary theories implicate Jupiter's intense radiation environment as the primary culprit. Onboard fault protection software was successful in keeping encounter operations going, although during one incident the spacecraft's tape recorder temporarily stopped recording. This error resulted in the truncation of the Fields and Particles Io Torus and Perijove recording, the loss of two Europa observations by the Near-Infrared Mapping Spectrometer, and the loss of the Plasma Wave instrument's observation of Chorus emissions (Chorus emissions are created when plasma is accelerated due to wave-particle interactions within Jupiter's magnetosphere).
The close flyby of Callisto occurs early on August 14, at 1:31 PDT and a distance of 2296 kilometers (1427 miles). The flyby will reduce the spacecraft's Perijove distance, or closest distance to Jupiter for a given orbit, from 7.3 Jupiter radii (523,000 kilometers, 325,000 miles) to 6.5 Jupiter radii (465,000 kilometers, 289,000 miles). The change in Perijove distance is not seen until Galileo's next encounter, however, because the Callisto flyby has occurred after this encounter's Perijove passage.
During the Callisto flyby, the spacecraft passes behind the moon as seen from the Sun and the Earth. As the spacecraft flies behind the moon, its radio signal will be weakened and refracted by Callisto's tenuous atmosphere. These changes will be measured by the Radio Science team back here on Earth, which will allow scientists to study the structure of Callisto's atmosphere. Galileo's last observation for this encounter is performed by the Ultraviolet Spectrometer. The observation looks at Ganymede while it is eclipsed from the Sun by Jupiter and hopes to capture auroral activity in action.
This week's playback schedule includes observations made by the Solid-State Imaging camera and the Near-Infrared Mapping Spectrometer, but first on the schedule is the return of a recording performed by the Fields and Particles instruments. The recording was performed for six hours as the spacecraft flew through the Io torus and Perijove. The measurements will contribute to the study of the dynamic processes that occur within these regions.
The Solid-State Imaging camera returns 16 observations this week. The first five contain images of Io, two others capture views of Amalthea, and the remaining nine look at Jupiter. The first four Io observations are part of a campaign designed to monitor volcanic plume activity on the moon. The remaining observation provides data on the size and shape of the volcanic moon.
The camera's observations of Amalthea will enhance studies of the shape of this inner moon. They will provide the best spatial resolution ever obtained of the moon (up to 8.5 kilometers, 5.3 miles, per picture element). Finally, the camera's observations of Jupiter are part of an extensive campaign designed to enable scientists to study the dynamics of cloud motion in Jupiter's atmosphere. The campaign includes examining nine different locations on Jupiter's globe and five different atmospheric features. This week's data return returns 9 of 34 total observations performed during the encounter.
The Near-Infrared Mapping Spectrometer fills the remaining time available in this week's playback plan. The observation returns measurements of a white oval in Jupiter's atmosphere. White ovals are long-lived storms that form between two adjacent zonal jet streams.
Note 1. All times listed correspond to the Pacific Time zone (currently daylight time) and spacecraft event time. Radio signals indicating that an event has occurred on the spacecraft reach the Earth 33 to 50 minutes later, depending on the time of year. Currently, Pacific Daylight Time (PDT) is 7 hours behind Greenwich Meridian Time (GMT), and it takes radio signals 38 minutes to travel between the spacecraft and Earth.
For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page.
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