Illustration of Galileo

NASA's Galileo spacecraft will fly by Jupiter's largest moon, Ganymede, for the fourth and final time on Wednesday, May 7.

The closest approach will take place at 8:56 a.m. Pacific Daylight Time as the craft travels 1,600 kilometers (994 miles) above Ganymede at a speed of 8.6 kilometers per second (more than 19,000 miles per hour).

During the encounter, Galileo will collect data on the moon's surface shape and atmosphere. High resolution studies by the craft's remote-sensing instruments will include observations of Osiris, a dome structure; Tiamat Sulcus, a region of craters, grooves and furrows; a multi-ringed structure; and caldera-like features and dark floor craters.

Galileo will also begin its second "mini-tour" of the Jovian magnetosphere to learn more about the composition and dynamics of this tremendously vast region around Jupiter controlled by the Jovian magnetic field. This second "mini-tour" will continue until the end of Galileo's primary mission on Dec. 7. The tour, to take place this summer, will include a deep penetration into Jupiter's magnetotail, the region of the magnetosphere opposite the Sun's direction.

During this encounter, Ganymede will block the spacecraft from the Earth and the Sun for about seven minutes. This will provide scientists with an opportunity to measure changes in the spacecraft's radio signal as it passes very close to Ganymede, but just before it's blocked out by the Jovian moon. These measurements will allow for further study of Ganymede's tenuous atmosphere.

In addition to being the largest of the Jovian satellites, Ganymede is the largest moon in the solar system. Although this marks Galileo's last encounter with Ganymede, the craft will fly by two other Jovian moons, Callisto and Europa, before its primary mission ends in December. A two-year extension of the Galileo mission will enable further studies of Europa and Io, depending on the spacecraft's health.

Galileo was launched in 1989 and entered orbit around Jupiter on Dec. 7, 1995. The Galileo mission is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC.

Images and other data received from Galileo can be found on the World Wide Web at

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