NASA's Galileo spacecraft will make an encore appearance at Jupiter's icy moon, Europa, on Thursday, Feb. 20, marking the closest planned Europa flyby of the initial two-year mission.
The encounter will be Galileo's closest flyby yet of Europa. The craft will swoop past the Jovian moon at an altitude of 580 kilometers (360 miles) on Thursday, Feb. 20, at 9:06 a.m. Pacific time (12:06 p.m. Eastern time).
Galileo made its first pass of Europa in December 1996, revealing remarkable detail of that moon's terrain. This week's flyby will look at other areas of Europa's surface, which is covered by ice and a series of criss-crossed, dark lines. Europa holds great fascination for scientists because of the possibility that liquid oceans may be hidden underneath the icy surface. The presence of liquid water would boost the odds that Europa could host some form of life.
"I think this flyby may provide additional clues regarding the prospect of liquid water oceans on Europa," said Galileo Mission Director Bob Mitchell.
With its diameter of 3,138 kilometers (1,946 miles), Europa is just slightly smaller than Earth's moon. Because the geometry of the upcoming flyby will be somewhat different from the path taken by Galileo's previous Europa encounter, it will yield data and images of different portions of the moon.
"This position will allow for high resolution of different terrain," said Mitchell. "It will help us learn more about Europa's structure and surface and how the surface was formed."
The current Europa encounter phase began on Sunday, Feb. 16, and will continue through Saturday, Feb. 22. The spacecraft has already begun returning real-time encounter data, with recorded data scheduled to be transmitted to Earth beginning on the evening of Saturday, Feb. 22 (Pacific time).
This encounter will include the return of magnetospheric measurements from Europa's vicinity. Other science highlights will include the study of surface features of Europa's lineated regions, images of two other, smaller Jovian moons, Thebe and Amalthea, and studies of such Jovian atmospheric features as the south equatorial belt-zone boundary and the aurora borealis.
This flyby provides a period of radio occultation, when Europa crosses between Earth and Galileo, temporarily cutting off the spacecraft's radio signal. This affords a prime opportunity for Galileo to study atmospheric data just before and after radio contact is lost, when the signal passes through the Europa's atmosphere.
"As the fifth encounter in Galileo's series of 10 flybys, this marks the approximate halfway point for this series, which began in June 1996," said Galileo Project Manager Bill O'Neil. "It's been eight months since then, and it will be another eight months before the series' final encounter."
A third Europa flyby is planned for Nov. 6, 1997, and JPL has asked NASA to extend the Galileo mission by two years to include eight more Europa flybys and ultimately a flyby of Io. The proposed extended mission might be shortened if the spacecraft's operations were to deteriorate as a result of its continuous exposure to Jupiter's extreme radiation environment.
"NASA has assured us that the extended mission will be funded," said O'Neil. "The $30 million needed for the extension will come from within the existing NASA budget, enabled by cost savings due to improved efficiencies in JPL's spacecraft tracking and mission operations."
The 2,223-kilogram (2-1/2 ton) Galileo orbiter spacecraft was launched aboard Space Shuttle Atlantis on October 18, 1989. JPL manages the Galileo Project for NASA's Office of Space Science, Washington, D.C.
Additional information on the Galileo mission and its results can be found on the World Wide Web at http://www.jpl.nasa.gov/galileo.
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