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This Week on Galileo?
May 22 - 28, 2000

Galileo's Instruments Focus on Jupiter's Aurora and Atmosphere

Jupiter continues to dominate Galileo's observation schedule on Monday as instruments focus on the planet's aurora and its atmosphere, including the Great Red Spot. The spacecraft makes its closest approach to Callisto at 4:39 p.m. PDT [see Note 1] Monday at a range of 331,000 kilometers (206,000 miles).

The first three observations of the week are spectral scans of Jupiter's bright limb, performed by the Near-Infrared Mapping Spectrometer (NIMS). Like observations performed on Sunday, May 21, these scans will be used to provide scientists with data on the bulge created at Jupiter's equator as Jupiter rotates once every 10 hours. NIMS follows these observations with a series of 10 spectral scans of Jupiter's north polar region. The series consists of 10-minute samples separated by 60 minutes, and is designed to capture auroral activity.

Interspersed with the aurora observations are three global observations performed by NIMS and three Great Red Spot observations performed by the Solid-State Imaging camera (SSI). Taken together, the global observations performed by NIMS will map a substantial proportion of the complete range of longitudes of the planet. The Great Red Spot observations performed by SSI will provide scientists with high spatial and time resolution images of this storm, which is over 400 years old. Similar observations were taken at the beginning of Galileo's orbital tour in June 1996, so scientists will be able to observe long-term changes in the characteristics of the Great Red Spot. The Great Red Spot is so large that the Earth fits two times across it!

A brief interlude from Jupiter is afforded to SSI to obtain a set of global images of Europa through four different color filters. The images will fill in a gap in existing global color coverage between 120 and 230 degrees longitude. Five more Jovian equatorial bulge observations are then performed by NIMS. The first three occur on Monday night, with the remaining two performed on Tuesday morning. Next, SSI takes a set of global images through different color filters that capture Europa while eclipsed from the Sun by Jupiter. The observation should help scientists search for auroral glows in Europa's tenuous atmosphere. These glows would be produced by the interaction of atmospheric gases with Jupiter's magnetosphere, and may produce current flow between Europa and Jupiter. The geometry and timing of this observation are superior to those of similar observations taken earlier in the mission.

SSI's eclipse observation brings to a close the bulk of this encounter's observing. In previous encounters, playback of recorded data was initiated at this point. But Galileo is not yet finished collecting data. The Fields and Particles instruments will continue observing for nearly one month. This will allow them to extend their typical survey of the inner magnetosphere (performed at each encounter) through the outer magnetosphere, and through the transition from inside Jupiter's vast magnetosphere into the solar wind. Some data will be returned in realtime and some will be placed on the tape recorder for return after the conclusion of the survey.

The survey is interrupted once during the remainder of the week. On Wednesday, the spacecraft will perform a flight path adjustment, if needed.

Note 1. Pacific Daylight Time (PDT) is 7 hours behind Greenwich Mean Time (GMT). The time when an event occurs at the spacecraft is known as Spacecraft Event Time (SCET). The time at which radio signals reach Earth indicating that an event has occurred is known as Earth Received Time (ERT). Currently, it takes Galileo's radio signals 50 minutes to travel between the spacecraft and Earth.

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Last updated 10/01/01.

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