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Galileo Millennium Mission Status
Galileo Millennium Mission Status
28 Dec 2000
(Source: Jet Propulsion Laboratory)

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NASA's Galileo spacecraft has successfully flown past Jupiter's moon Ganymede, the largest moon in the solar system, while Ganymede was eclipsed in Jupiter's shadow.

Engineers at JPL said that Galileo dipped within 2,337 kilometers (1,452 miles) of the surface at 12:25 a.m. PST today. A passage during Ganymede's eclipse was planned in order to observe auroral glows in that moon's thin atmosphere.

"It looks like a nice, calm flyby," said Jim Erickson, Galileo project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The team was prepared for problems, but we're happy without any. And we'll be even happier once we've passed this orbit's closest approach to Jupiter."

Intense radiation near Jupiter poses a risk to the spacecraft's electronics. Galileo's closest approach to Jupiter on this orbit will come at 7:26 p.m. PST tonight. Information about the status of the spacecraft at that point should be received on the ground about 35 minutes later, via radio signals traveling at the speed of light. The last time Galileo passed close to Jupiter was in May 2000.

Galileo has already received three times the cumulative radiation exposure it was designed to withstand and has continued making valuable scientific observations more than three years after its original two-year mission in orbit around Jupiter.

At 1 a.m. today, mission controllers at JPL received the signals indicating that the Ganymede flyby had taken place. The signals had been relayed from the Goldstone, Calif., and Madrid, Spain, stations of NASA's Deep Space Network, which operates large dish antennas around the world for communications with spacecraft.

Galileo's camera and other instruments were set to capture the flyby with images and other observations. If all goes as planned, the data will be transmitted to Earth over the next five months for processing and analysis.

As of 9 a.m. today, the spacecraft had recorded 31 percent of the scientific data that its instruments had been programmed to collect during this swing through the inner portion of the Jovian system, from Dec. 26 through Dec. 31. Besides studying Ganymede, Galileo is making more distant observations this week of Jupiter and the moons Io, Callisto and Europa. Some of the observations are planned as part of collaborative studies with NASA's Cassini spacecraft, which will pass Jupiter on Saturday, though at a much greater distance than Galileo is from the planet this week.

Gases in portions of Ganymede's thin atmosphere give off a shimmering auroral glow as they are struck by electrons from Jupiter's radiation belts. The phenomenon is similar to Earth's Northern Lights and to what happens inside a fluorescent light bulbs. Sunlight washes out the glow, so Galileo scientists took advantage of the eclipse to study the glow for information about the chemical makeup of the gases and the structure of Ganymede's magnetic field, which affects the location of the glow.

Ganymede is the largest moon in the solar system, larger than the planets Mercury and Pluto. It is also the only moon known to have its own internally generated magnetic field. Earlier this month, scientists announced evidence that Ganymede may have a thick layer of melted, salty water under its ice-rich surface.

"Ganymede is certainly one of the most interesting places in the solar system, and we're looking forward to see what kind of new surprises Galileo may have to tell us about it," Erickson said.

Additional information about the Galileo mission is available at

Galileo was launched from NASA's Space Shuttle Atlantis on Oct. 18, 1989. It began orbiting Jupiter on Dec. 7, 1995. JPL, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C.

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Last Updated: 5 Jun 2001